How long does it take to lose steroid weight?

There was no forum for dermatomyositis which is what I'm diagnosed with, but its quite similar to lupus so I figured post it here. I was diagnosed on October 1st and was put on 40mg of steroids everyday for 3 months I'm now tapering down by 5mg a month. I wasn't gaining weight at first, but I weighed myself just before Christmas, and saw I had gone from 12 stone 7 pounds to 13 stone 4 pounds. This was traumatic for me as I've always had problems with my weight in only 16 and I've had a lot of mental problems relating to weight very insecure and that kind of thing. I'm now on 25mg a day and i weighed myself today because I thought id start loosing, but I've gained another 4 pounds! I've been eating as healthy as I can, and walking as much as possible I should be off the steroids by April. But how long will it take for swelling to go down and lose the weight its really getting me down.. Please help?
Also on chemotherapy weekly injections of methatrexate
1 Vitamin D tablet a day
25mg of prednisone a day
1 lymacide tablet a day

I have done three rounds of steroids each time for about six weeks... I usually feel myself about three to four weeks later. I try to watch while on them and get in exercise and weights when I can. I know why can't the side effect be losing weight.. Just once!!