Lumps and bumps that suddenly appear are usually infections. If due to bacteria, it usually resolves by rupture (like a boil) pretty quickly. The white liquid that oozes out is pus that is formed when the white blood cells ( immune cells) die while killing bacteria (in general). DO NOT TRY TO POP OR SQUEEZE THE LUMP. Like a boil in humans, squeezing can cause regurgitation of the pus into the blood stream of the fish with deadly results. It is also not a good idea to seal a draining wound unless it is bleeding. The most common bacteria of GF is Columnaris and aeromonas.
Wounds that are white on the edges and red in the center are aeromonas. Those that are red on the edges and white in the center are generally columnaris. Both are gram negative bacteria TMP-4 is a sulfa antibiotic with trimethoprim which can be put in the water and mixed with food (that is what Romet B is). It is still effective against most, but not all gram negatives bacteria.
It is very important to move fish with wounds to a new bucket of freshly aged and salted water every day to move them away from bacteria and/or parasites in the water.