I've never taken prednisone long-term, but my mother has. Every single time she came off it she lost her moon face pretty quickly. I know that I was on prednisone for a week. When I came down off it, I lost 8 pounds in one week (gained 6 the week I was on it). At least some of your extra weight is probably water retention--this will certainly go away quickly.
I'm curious about your mtx side effects. You mention hair loss and fatigue? Hair loss, at least, is associated with a disruption in your folic acid pathways. So, if you're taking folic acid that should help with hair loss overall. My rheumy said if I ever start getting mouth ulcers or hair loss, just increase the folic acid I'm currently taking. I only take 1mg/day, but he told me he has patients that take up to 5 mg/day. If you're not taking folic acid, you really need to call your rheumy and ask why not. If you are taking it, consider increasing the dose.
Current dx: Rheumatoid Arthritis
Suspected dx: UCTD/Early Lupus
Current Meds: Enbrel, Plaquenil, Aciphex, Ultracet, Zyrtec, Allavert-D, Zantac, Tylenol PM
Past Meds: Relafen, Vioxx, Mobic, Voltaren, Sulfasalazine, Entocort, Prednisone, Humira, Reglan