What could this be??

Hello, Ive looked around online for this, i found alot of answers but couldnt really I.D. it. I got this fish about 5 days ago, there was no bump on day one but on day two it started as a small speck like a nibble. Then on day 4 the bump got bigger and he seemed to be in the dying stage. Short breath, couldn't really swim, floated on his side, the this morning hes up like nothing wrongs with him, but the lump is even bigger (picture). Should I be worried? What do i do?



Thanks :cry: