If it were me, I'd stay on the prednisone until the mtx is starting to work - but you'll have to talk to your specialist about that.

The weight gain is quite simply down to the prednisone. In my experience, while on prednisone you gain weight. Exercising and watching your diet can slow it, but I've never been able to reverse it until I'm off it. I imagine at your dosages it would be fairly similar. I don't think the mtx will help with weight loss on its own, but it should allow you to get off the pred and make it easier to lose weight. I've also been stacking on the weight (even without pred!) and now find myself weighing the same as my highest weight during pregnancy. It's depressing, but I'm now getting to the point where I can start exercising again - need to start slow and gently, but I know I can start to do something about it now.

BW