Why is my fish spitting out all of its food?

I got an oscar a few days ago. I got her free from Wal-Mart because she was in rough shape and I was close to tears, so the manager of the fish department just gave her to me. The other oscars were nipping at her fins and they are still very damaged.

I’m keeping her in a small tank (less than 5 gallons) until her fins are better, then I’ll move her in with the other fish (4 barbs and a rainbow shark) in the 15 gallon tank. I’ve been watching her behavior and I noticed:

•she is spending a lot of time just sitting at the bottom of the tank in a corner.
•She is having color changes (green to black)
•I saw 3 white spots on her side, but I didn’t think much of it, because it looks like it’s just part of her coloring, but I guess it could be Ich…
•And the part that is bothering me the most is that she is spitting out every bit of her food. I tried both flakes and pellets. She’ll chew it up and spit it all out. She’s still very young, so I don’t think she can eat any live food now, and I read up on it and said at this age they’ll eat flakes an pellets (and mine are infused with shrimp).

I’m just not sure what exactly is wrong… I’m going to buy some bacterial medicine soon, but I’m not even sure if that’s what she has. Sorry for the life story of my oscar (^_^;;).

Thank you so much for taking your time to help!!
Yes, I know it’s bad that I’m keeping her like this, but I’m not planning on having this fish for long. She was NOT better off there. It was really awful. I’m preparing a 10 gallon tank now for her, and when she’s better I’m giving her to a friend of mine who keeps fish. For now, it’d be nice to help me instead of criticizing me. I’m just trying to help my oscar…

But anyway, I do thank you all for caring.

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