Dear Noah, when you first posted for help for "schizophrenia" - one responder started their post with "Legion". That could potentially put 'that' thought into your mind.
There are two words in your post that come from false teaching about what can happen to "Christians".
Those two words are "in" and "cast out".
You need to read The WORD of GOD to see where a truly Saved Christian stands in Christ.
No where in the entire New Testament will you find demons "In" a Christian - needing to be "cast 'out'".
If you truly gave your life to Christ and experienced true conversion - yes - demons can lie to you, in your mind.
They can put thoughts into your mind - Yes.
They Especially work with and thrive on "fear" and false doctrines.
They especially work through "lying to a child of GOD" that Christ's initial entrance into their spirit is Not Enough.
I watched as a young lady who had the fear of displeasing GOD and saw 'every thought' that she had that wasn't perfect, turn to a "deliverance minister" who held her chin back [which chokes a person] and he kept yelling at her "name yourself - name yourself" and the poor innocent girl could only speak what she feared. She feared every thought that wasn't 'perfect' so she named "lust" - "fear" and anything she could think of.
This man and his helpers 'thought' that those were demons 'naming themselves'.
When she finally was too exhausted to continue naming things and actually ran out of things that she thought were sinful - they let her go. She was just so pleased that they finally let go of her throat that she Praised GOD.
Her heart was tender toward The LORD and she loved Him more than life --- but when she got home - a fear took over her and in came the enemy's words into her mind - "We're still in here."
Well - this has a very happy ending, because a Stronger Voice came next and said - "Go Read MY WORD" and Jesus in His Tender Mercy directed her to Scripture after Scripture and More Scripture of where a true Saint who desires to please Him, Stands in Christ - "GOD our Saviour", and that what these men were believing were Dead Wrong.
She became a very strong child of GOD - able to minister His Truth to others bound by sin and fears, by leading them through the WORD of GOD which sets us free from sin and fear by His Spirit of Truth - The Power of The Holy Spirit - with the gifts of The Spirit - through Counseling by His Spirit Whom He called our "Comforter".
How did this girl think that she needed things "cast 'out' that were 'in' her" ... only by the teaching of men - Not from her Bible.
Only the Unsaved have demons "in" them. HE - The LORD of Glory has "swept the house clean" when He took ownership of that house.
Unless a person is in complete rebellion against GOD in practicing sin as a lifestyle, will they be later tormented - which is a type of chastisement for a True Saint to scare the sin out of them. I've testimonies of people who weren't saved that had demons "scare the hell out of them" and they dropped to their knees and cried out to GOD ... :) ... because people had prayed for their Salvation along the way.
If a person hasn't made a true commitment to GOD toward salvation - well, then, that's a totally different story.
How do we know if we've made a true commitment to GOD onto being Saved by Him - by the fruit of the change in our lives. We don't become perfect - but we do see a change in the things that we once practiced and desired. We can feel that change in heart and desires.
Yes, many say a prayer but never have any change in their desires - so yes, they need to truly get down to business in coming in sincerity To The LORD GOD, In Truth --- but if they have sincerely come to Him and have experienced the evidence of salvation - then they need to shout back at the devil - I'VE BEEN CLEANED OUT OF ANY DEMONIC SPIRITS BECAUSE NOW, THE 'HOLY' SPIRIT RESIDES IN ME AND NO DEMON CAN BY ANY MEANS RESIDE IN THE "SAME TEMPLE WITH" THE SPIRIT OF THE LIVING GOD - THE CREATOR OF 'ALL' THINGS - INCLUDING FALLEN ANGELS.
After which - you come to realize, that all that Satan and demons can do is 'vex' you with their "lies" AGAINST GOD'S WORD, and of WHO HE IS and especially of what HE HAS DONE WHEN HE "SAVED" you.
Oh Happy Day when that realization hits us!!
From then on - you know that all attacks on you are coming from the outside in ... just as Satan spoke to Jesus in the wilderness - and How Jesus showed us how to fight Satan - is with The WORD of GOD alone!
The lies Against GOD are that when He saves - He doesn't do a very good job in cleaning house. Can you see that?
Our "attacks" come from the Outside. We are fed lies, temptations, wrong thoughts about GOD, errors in beliefs/false doctrines, and so forth from the outside - from the enemy feeding thoughts into our minds - from the outside. They Don't Live IN a Child of GOD! and THAT's Scripture!
But we choose what we believe. His WORD is there for us to set us Free - if we'd just believe it.
My prayers and the prayers of others who want you to see Jesus as GOD Almighty Himself that Loves you, are with you 100%.
Battle any off-thought with His Word and fight against the labels that men and demons put on you.
The battlefield is the mind.
We need to take 'every' thought captive to the obedience of Christ - which means - filling our minds with His WORD, so that His WORD becomes the only thing in your mind. After a while - your thinking is replaced with thinking in Scripture. Scripture becomes your new way of thinking. Everything is filtered through Scripture alone. At that point - error is caught immediately when heard and immediately tossed by the WORD alone. ie "...The Joy of The LORD 'is' our Strength" and He wants to bring us into that joy.
Hand-write all of the positive verses you can find from the New Testament. There is a benefit in writing them out by hand. Avoid things secular, like TV and whatever feeds the flesh. Keep good Christian music on and if you have the New Testament on CD, then listen to that also.
The Old Testament Points to Christ Who is found in the N.T. with all of His Words of our complete victory over injected thoughts.
Until a person learns the New Testament and it becomes a solid part of them - I always give struggling or new Christians just the N.T. and Psalms - until they are totally built up and can understand how to use the O.T. properly. Which parts apply to the Spirit filled Christian and which are Pre-Christ.
Bless you Noah with every spiritual gift in Christ Jesus our LORD. Please Trust in HIS WORD alone - in Jesus' Authority, Amen.