Okay, I’m not a doctor, first of all. Questions like these should definitely be directed to them, but I’ll do my best to help you out.
Opinions differ on this, but in my experience, generics are the same as brand-name drugs. As long as the chemical name of the drug is the same, you should be fine. So according to my googling (!) quetiapine is the generic for seroquel, meaning both have the same chemical name so it should be fine.
Psychiatric medication does take a while to really get moving, but the maximum is supposed to be like, two months. If your medication isn’t working after a year, it is probably time to go back to the doctor and try a new one.
Take care of yourself,