Sick African Dwarf Frog?

Anyone have any experience with sick ADF's? I've had two for nearly two years now, and never had any health problems... until now I believe.

One of my ADF's looks bloated, like it has a balloon under the skin. This is located on the left side, from under the arm to the hip. It is still actively swimming (as well as it can with a huge bulge under it's arm), and does not have any other external symptoms that I have noticed.

Is my frog actually sick, or could this possibly be from over eating or some other cause? I'm at a loss, so any suggestions are welcome!

Thanks!

Oh, and the frogs live together with two otos in a 2.5gal hex with an UGF. And I feed them frog pellets by HBH.

In some ways I hope it is a tumor - that way it wouldn't be something it'll pass on to the other frog.

I didn't feed them today in the hopes that the 'bloatiness' would go down, but it looks the same as yesterday, so I'm just keeping an eye out for now... I don't have any ideas as far as medication though. Maybe whatever it is is non-fatal.