What’s wrong with my Australian Rainbow

I don’t see where I can upload pictures, so I’ll describe as best as possible… the lump is white/grey in color; it’s located behind the stomach cavity but before the tail… in the flesh; the lump can be seen if looking down on the fish; the fish doesn’t seem to be bothered by it… eating & swimming normally; 1 lump; could’ve been on her at the store, just didn’t notice it.
Any suggestions welcome.