My pet can't battle whenever I try there is a message that says: "Oh no! None of your pets are eligible for battle. You might want to make sure that they're well fed and happy!" But it is bloated, very happy, has full health, and is not training or in the resort.

Is it stuck in a battle? If not, you could probably file a ticket about it because the UAs can check it out.

http://subeta.net/games/battle/stats.php

haha thanks that was the problem. I haven't been on in a year or so, so I forgot some stuff.

lol no problem. I had to actually remember what link it was myself.