Toxic psychosis isn't necessarily something that can be fixed on your own. If it's that prominent and hasn't gone away yet, I would definitely recommend real medical attention. They may prescribe anti-psychotics or other forms of treatment such as psychotherapy.
600 mg doesn't sound like a very high dose for most people, or at least not one that usually causes psychosis with repeated use (usually 1500mg/day is the amount taken that triggers psychosis) and it shouldn't last 2 years even if it is temporary drug-induced psychosis, so you should really get that checked out...
best of luck!!