I understand your concern. Weight gain while on treatment for bipolar disorder may be due to a variety of reasons. More clarity is needed regarding your problem. It is unclear if your
thyroid levels are normal. However it is easily manageable with appropriate treatment, so that dysfunction due to the same can be reduced and your quality of life will improve. Some counselling sessions along with medical help might be useful for you. Lamotrigine is an alternative drug however whether it can be used in a particular individual is decided based on a lot of factors. I would also be more than happy to help you with that if you are looking for further online assistance. You can directly consult with me through Practo as needed. Online chat consultation is available.