Please help me diagnose my fish!?

Hi, one of my pearl danios is really ill and I have no idea what to do! It has an ulcer near it's tail and that has been the same for about 4 days, I have tried to treat it with melafix but it has only scabbed over, nothing else. It also has a severely bent back. Also the top of it's body had a white spot and it also had one on it's side but that has now gone, and the scales at the top are starting to go funny and look like their loose. I thought it was dropsy but now I think it's scoliosis or fish tb. What is it? Please help and tell me how I can cure him. Thanks!