Platy sick

Question
QUESTION: For starters, my platy was swimming awkwardly so separated it from the rest of the tank. It was VERY red around the poop hole area. It started swimming upside down, then right, then back upside down. While separated I have melafixed and done water changes, etc. It began swimming normal again, but still have it separate. It's finally eating, and pooping...but is still red in that area. Also now the back fin tip is white...is there any hope for this fish? Is there anything I can do? Should I just leave it separated from the rest?
Thanks in advance.
ANSWER: The swimming awkwardly is Swim Bladder but that is usually a sign that something is seriously wrong. The reddened area sounds like a parasite, please answer the following questions:
Anything hanging from the anus?
Concave belly?
Fish scrapes against anything?
Mucus covering the body?

After you answer those questions, I should be able to determine what if any parasite your fish has.

---------- FOLLOW-UP ----------

QUESTION: The first couple days separated it wouldn't eat, and yes there was something I assumed was poop hanging. I cannot tell now, it's swimming better and won't stay still. The fins down there near the red area don't go down, they stay against the fish's body, so that doesn't help either.
No concave belly.
Does not scrape on anything in tank.
No mucus on body, fins, etc.
Just the white on the tip of the back fin.

Answer
It's Nematoda. It's a parasite that hangs out the fish's rear. There are a couple of ways to treat this:
-Antifluke medication
-soak the food in parachlorometaxylenol and give the fish a bath
-treat the aquarium with 10 ml per liter. The bath should last for several days
-find special food containing thiabendazole as a nematode (threadworm) cure and hope the fish will eat it