Dilantin and weight gain

I have been taking dilantin as a stabilizer for bipolar disorder. I was told that it would cause me to feel sleepy, which is fine with me because that really helpful with the whole insomnia thing. I just take it before bed. I noticed that at first I felt like I was walking through a perpetual fog. But that seems to have stopped now. It seems to be working ok. My problem is it seems to have increased my appetite and caused me to gain weight.
I was wondering if anyone else had noticed substantial weight gain (3-10 lbs in 2 weeks!! :( ) . I've read that a lot of people experience weight loss with dilantin, i was wondering if the opposite could be true as well.