You didn't say your frog looked fat; that's normal. You said it couldn't walk without pushing itself around on its back legs.
The reason I thought you were trolling was because that first post seemed to say that your frog couldn't walk. Then you did not post the information asked for. You said you keep it on "coconut substrate" and that it was looking "a bit funky". There is no way ANYONE could give any helpful advice based on that, not even a trained vet.
Sorry for misinterpreting, but if you think your frog might have a health problem it is important to be as detailed as possible.
It would still be good to post the information I asked for and a picture, so people can tell you whether anything in your care routine or diet could be causing the frog to look bloated or become obese. Otherwise, all anyone can tell you is that these frogs are supposed to look 'fat' due to all the water they retain. They can't give you any information on whether the frog is retaining too much fluid or is unhealthily fat without more info and/or pictures.
I'm still confused. In your first post you said your frog "literally uses its back legs to kind of push itself". Now you're saying that the only problem is that you can't really see the frog's front legs when it's sitting still. Which is it? I just want to be certain, because the first is a potentially fatal health problem, and the second is nothing to worry about.