hi..thanks for the query.
You are probably gaining weight because of the intake of Oral steroid
medicine .However ,currently that is the right choice of treatment,hence I would advise you to continue the same.It will help you regain the growth of hair.You can also take in Biotin
tablets and apply topical Minoxidil
2-5% solution for faster regrowth.
Hairloss ,if progressive over the years,also take months-years to regrow well.Hence ,continue the treatment with regular follow ups and changes if required.Increase protein intake as this will help in regrowth as well as substitute fat/carbohydrates to help not gain too much of weight.