Weight Gain on Epilim

I am a 24 year old female. I was diagnosed with juvenile clonic tonic epilepsy when i was 11 years old. since then I have been on Epilim. my dosage has changed here and there but I am now on 1200mg a day.. since being on epilim i have found that i have been gaining weight slowly.. i am now at a stage where i cannot handle it anymore. I exercise regularly minimum 5 times a week sometimes even 7 times a week. i have a spinning bike, i swim around 1.7km when i do swim and that is between 2-3 times a week. 3 times a week i take boxing classes and i do yoga once a week. i have an active life style and an active job.. im a teacher. I have never been a big eater, my portions have always been small and i watch what i eat.. i have been on diets, weigh less programs etc but i can never seem to lose weight. i have recently heard about epilim being a nightmare for women as it makes you gain weight.. i cannot for the life of me lose weight.. maybe a kg here and there but thats it. and the emotional struggle this has been for me is getting too much. my neurologist says epilim is my only option because of the type of epilepsy i have. is this true? is there anyone else experiencing this problem? what solutions are out there?