Your fustration will only fustrate you further. Whenever I run into a wall, I jot down my thoughts and note my feelings on the subject I'm wanting to write about then I shelf it for about two weeks to a month, do a review and see if I can take off from where I left off. If not repeat the process. I find that if I'm trying to write to impress, I fall flat on my face. Do it because it stirs your heart, do it to lift somebody up, to help, to comfort, mostly to glorify God.
You mentioned mental illness,...God through Jesus Christ has given you power to overcome anything and everything, don't use that as an excuse, Romans 6:6-7. PUSH through it!! Romans 8:28 (READ the whole verse) Sometimes, we as christians like to only read the fun parts and ignore what our part requires. Also Philippans 4:13. Finally Philipppans 4:8, You are responsible for thoughts you allow to remain in your mind. Listen, when God said the truth will set you free, He knew exactly what He was talking about. Been there done that.
Brother, I am not meaning to beat you up, but build you up with God's word. Remember P.U.S.H., Pray Until Something Happens!
God bless, Donna