You're on a whopping dose at 20 mg and it's no wonder you're gaining. It will probably level out though, you just have to give it time and keep watching what you're eating and when you're eating. Try not to eat after 7 PM, all those calories do is sit there since you're not likely exercising at that hour. And speaking of exercise, try to find something you enjoy, like dancing around the house to rock or hip-hop, swimming, just something you'll actually do. I'm like you, I'd rather be stung by 1000 hornets than work out. But I don't mind sweeping and vacuuming, and I can make exercise out of gardening, and those things count as movement in my book.

If that doesn't help control the weight gain, you can always talk to your pdoc about reducing the dose. Like I said, 20 mg is a LOT (the most common dose is 5-10 mg) and if you're in the middle of a crisis you may need it for now, but once you've settled down the dose might be lowered. Just throwing that out there...best of luck.