Lump On Swordtail

OK so I have been having some problems for the past week with my tank. I treated for what I thought was ICH, ended up losing 2 fish, did water changes, and I thought I was on my way to recovery, no other losses. Last night I noticed something that looked like a lump on my swordtail's head. It's behind the eye, above the black horizontal stripe on his body. He seems otherwise normal, no clamped fins, swimming, eating, toilting looks ok, belly looks ok, just this lump. My water parameters are within normal limits and today is my normal gravel vac and water change day. Took a pic, he wouldn't stop swimming its blurry but you can still sort of make it out. It looks shiny but is not discolored

The lump has grown since last night. It is roughly the diameter of a large pea and sticks out about thalf the width of a pea. Any ideas?

Can you issolate the sick fish.
Does the lump look like its filled with fluid or hard looking.
Lumps that suddenly appear are usually bacterial.
Best to issolate fish as if the lumps bursts in can infect the tank.

it actually appears to be filled with pus (but then again, the lump is white and so is the fish...) I have a plastic 5 gal terrarium with a lid that I could put him in as my 10gal is filled with fry. Would he be ok in there without a heater? I have some maracyn that I could treat him with.

You really need a heater as unstable temp can cause desease.
is it possilbe to got out and buy a heater.