Best exercise to lose belly + weight...?

So after having my daughter I went on the nexplanon implant which made me gain 34 pounds in 2 months! I barely had stretch marks from my pregnancy but after getting on that birth control I have stretch marks all over my upper arms, thighs, butt, belly, breast...you name it. I look and feel awful. I switch birth controls and am trying to eat better. I also take green tea pills to help me lose weight. What would work best to get rid of belly fat? I can't really go for walks.. I have no one to watch my daughter and I live in MAINE so its way to cold to bring out my 9 month for a walk.