My betta is in a 3 gallon heated tank. Last week after doing 100% water change I noticed a lump on his one side just behind his head and above his fin. I can't say for sure it wasn't there before I did the water change, but I'm thinking maybe when I cupped him he hit the lip of the cup? The bump has been there for almost 7 days. Is there something I can do for him? Could it be something other that him hitting the cup? Other than the lump, he's acting fine and seems healthy.