I know you are worried hun

. Its a worry when fish behave differently but I still dont think we have 911 here. I'm going to link you to Uberleslies thread that shows pics of her fish and how the same grey patches, piping, red spots, missing scales and loose skin all in the end went back to water issues which you are slowly learning about and correcting just as she did. The nitrogen cycle is what its all about with fish and its very important to follow a cycle with test kits and testing the water daily so that you know the peak danger points and can address them one at a time. If you had ammonia during the prazi treatment for example that would have produced the red spots.
You have done a huge long course of prazi. Time to finish that. You have done salt, time to finish that. You have fed Jungle food.
Your fish lives alone and you do not have any other tanks from which transfer of bacteria or parasites is possible. All the symptoms on your fish (except the lump) are what I call wear and tear. Its very stressful for fish to
move tanks/to be medicated/ to have change-except water change- in their lives. The affect stress has on the osmotic ability of fish to flush toxins is HUGE. Experts like Noga believe stress and disease in fish are inseparable, I agree. Stress certainly can cause diarrohea and strange poo too.
The lump.I have to say I am stumped here. Im sorry I just dont have a 100% sure answer about it. It could be a benign growth. You said it had turned black inside? This black could be from meds or ammonia. I cannot imagine this lump is still related to parasites because of the intensive prazi treatment. I even doubt its bacterial at this point. It could be viral- related to stress.Each time stress is experienced the lump returns or increases in size. That would be my guess right now.
You should focus on removing stress. Sustained good water conditions and a nutritious diet. Its not a cop out, it is everything for fish. Medication knocks immunity, you need to build it up.
PS Sorry not to get back fast on the PM, trying to find a house. Seems nothing is quite right, school district/rooms/price etc..very frustrating.