I'm on Seroquel XR 150mg(and Deprevix 150mg) and my weight hasn't changed much. If anything, I have lost around 5 pounds since I started taking it.

For the record I was already underweight before taking Seroquel, so it would be easier to put on weight if it caused weight gain.

Idk, are you sure that your weight gain is caused by the meds?
Have you checked your thyroid?
It really affects sleep though. One day I forgot to take my meds and I litteraly didn't sleep all night. Pure torture.