depakote to lamictal to depakote???

My 16 year old son had been on Depakote ER since he was 2 years old. His seizures were very well controlled unless he were to hit his head then he would have a grand mal seizure. When he reached puberty he gradually gained weight. He got up to 215 lbs. and he's only 5'10". He never exercised and he ate a lot! We decided to change his meds to lamictal (900 mg.), work with a personal trainer 3 times a week, and change his eating habits. He currently weighs 192lbs and looks great and his self esteem is so much better! BUT he's had 4 breakthrough seizures - the last seizure resulted in a horrible faceplant and I was sick to my stomach when I saw him; I felt so guilty. He also started having double vision and his mouth is dry all the time. His Dr. recommended he try Keppra or Zonegran. I want him to go back to the Depakote ER and this time we will do all we can to help him maintain his weight. Does being on Depakote mean you will gain weight inspite of diet and exercise? He obviously doesn't want to have anymore seizures, but he's afraid he'll put the pounds back on. Plus, I don't like what I've been reading on Zonegran or Keppra. I am sitting on the fence on what to do.