One of the horrible side effects of mood stabilizers and anti depressants is weight gain. Why that is I have no idea but it is not uncommon. Make sure your doctor knows what you are going through and see if she can tweak the meds to find a better fit for you. But don't just stop taking them on your own.
It took me 9 years to get stable after my diagnosis. Along the way some meds worked and some didn't. I had a lot of side effects... dead thyroid from lithium... and a lot of others including weight gain. I went off meds a few times and it was really bad for me. A new doctor finally took the time to evaluate me and my medical history and was able to come up with a new mix of meds that has been really good for me. But it took time and persistence.
Be sure to share everything you are feeling and experiencing with your doctor. If we aren't honest with them we will likely never get the right treatment. Your doctor is making recommendations but in the end you are the patient and it is your life. Try to be more assertive with the meds and work with the doctor. If you don't want a particular drug maybe they can find something else.
I hope you can find the right mix for you that will help you get to where you want to be.

Peace,
Mac