Welcome and congrats on your sober time!
I don't have any experience with these drugs either but wondered if the weight gain is something that happened almost overnight since you indicated that you just recently left treatment. No weight gain in treatment? Any dr. involved who could answer?
I'd post this on the substance abuse forum too - it may have already been asked and answered so some searching over there might shed some light on your question, but I'd ask again anyway. Take care.