I'm dealing with the same thing, and taking probably the same medication. Although I've only gained about 7 pounds, it's all in the belly/back area which is common with medication that suppresses all estrogen.I'm still weight training and riding my road bike about 100 weekly. I also have a Great Pyrenees who I walk twice daily and do HIIT at least 2 times a week. My diet is fairly clean so I'm kind of glad the weight gain hasn't been greater.
I'm more bummed about the hand and joint pain and the neuropathy that feels like electric shocks that run from my hips to my ankles. I can do only a couple sets of squats or lunges before the pain forces me to quit.