What is wrong with my guppy :( ?

About 2 weeks ago I noticed that maybe he was acting a little different but I guess I was too busy to really think anything of it. The tank had ich but only one fish had the spots and I treated the whole tank and everyone is fine but now, a week later, I noticed that one of the other fish bit off my guppies tail fin. This is weird because they have all been together for more than a month with no problems which is why I think they are picking on him cause he is sick. He looks kinda skinny too. All the other fish are acting normal so I took him out and put him in his own 5 gallon. He is swimming around and he picked up a flake and ate some but spit out the rest and now he is just swimmin around. I have melafix in there with him so he has meds for his fins. I also noticed that there is like a spot by his front fins on both sides of his body in the same spot on both sides. It is kind of a reddish gold color. Maybe it was there before and I didn't notice? Otherwise, what could it be? I have parasite medication, ich meds, and Melafix/Bettafix but I don't think any of those will help him. I think he has velvet or a parasite. What do you think? He is not showing signs of having trouble breathing or swimming either. I cannot test the water until tomorrow but last time I checked the level were all perfect (about a week ago).