I too am on 100mg of doxepin daily. I have also gain around 40 - 50 pounds. I used this medicine for migraines headaches. It didn't matter how much I ate or how much I exercised it seemed to just packed it on anyway. I went to the Dr. last month and he told me he would give me a prescription to help with the food cravings and that didn't work. The scales went up again.
So I went back to the Dr. yesterday and told him I wanted off the doxepin. He is taking me off it and now I will be trying different medicines to try to keep my migraines under control. Good luck!!!