The dose you are on are well below therapeutic dosages for psychosis. It is quite possible you have taken this dose and have it work as a placebo.

25mg of seroquel is the lowest tablet form you can get. Its unlikely you will get many side effects from such a low dose, besides sedation of course. It will not help with voices or depression at this dose.

CBT is great for all mental illness in my opinion, it can help with a variety of symptoms.

Are you off the drugs that induced psychosis now? Drug induced psychosis is not always a life sentence to mental illness. If you are clean you may well be fine off the meds too.