Lamictal and weight loss?

I have epilepsy and I know one of the side effects is weight gain. I remember when i first started to take it my doctor said it was like a steroid. I take 200g in the morning and 300g at night. The longest I have went without a seizure is one year and a half, so I do actually like being on this medication, it has proven to be the most effective for me.

The only problem I have is if it is preventing me to lose weight? I started taking Lamictal when I was 14 and weighed 125 pounds; now I'm 19 an weigh 167 pounds. When I used to do netball, boxing and swimming from ages 11 to 14 and a half. Epilepsy made me not want to do anything but long walks.

My mum found old photographs and I saw what I used to look like, I had a jawline, I was wearing a bikini on holiday with pride. It made me feel physically sick. I decided from there that I would start to lose weight, to be able to wear a bikini on holiday this September.

I started going to a Zumba class, I went everyday of the week and I also cut down on my eating habits, I stopped eating sweets, I had my food put on a smaller plate and I was drinking 6-7 pints of water. I had only lost 4 pounds in a month (a pound each week). On average the rest of the class had lost on average 20 pounds in a month (5 pounds a week)

I just want to know is Lamictal preventing the weight loss?