Lamictal and fats

I've been on Lamictal since December, i started out with 25mg, then to 50mg and now at 100mg which is where my doctor said I should be. I am taking Lamictal for a seizure disorder. Now I'm not bashing the drug but when I was taking 25 and 50mgs it was fine, I loved it. Seemed to work instantly. But now that I'm at 100mg the weight gain problem started. I have always tried to watch my weight so the only thing i can blame for not being able to take the weight off now is the Lamictal. I have been eating right, got back into the gym, watch my caloric intake as well as fats and carbs. Seems like for every pound i lose i gain right back in a day, it is awful. I did go thru a bad depression around the beginning of the year which I gained some weight from, but trying to get it off now is the hardest I've ever tried in my life. I am now 20 lbs heavier than I was since December. Has anyone experience this? And please tell me the outcome. I want to know if its me or is that a common effect that is now really greatly expressed as a side effect.