Lumps are tough, because it's hard to tell what they. I hope that this is one of those silly lumps that is nothing, and hopefully your vet will have a good idea. Your vet may want to get a sample and send it off to the lab. My girl's hard moveable lump was a mast cell tumor. My boy's was a benign cyst.
sure hope it's nothing, and hope that things get better for you - I know what it's like when everything goes south all at once