Try using conditioned tap water-- a bottle of Prime conditioner doesn't cost much and lasts for MONTHS, especially with only one animal. I lost a fish after only a month of living with untreated spring water (well situation) and believe it contributed in-part to some serious health issues with my pac too. She's doing great now, but it was pretty bad initially.

Also, how are you tong-feeding? When I first started my girl with tongs, I had to rub a worm between her lips for a minute before she'd get annoyed and take it. Sometimes they get scared without realizing it's food. I'd recommend trying treated tap water and also rubbing food against your frog's lips till he/she gets annoyed and bites a time or two (worms are less likely to scratch their skin when you rub their face IMO). They are often more eager to try tong-feeding once they realize there is food involved and not just metal "INSTRUMENTS OF DEATH" (as my python and White's tree frog like to call them).

But as others have said, plz post pics of your frog unburied. If he/she is toxing out, there are some quick/simple treatments you'd want to try. Like Lija said, soaking in luke-warm treated water with a couple drops of natural honey is great. It's like a natural laxative and encourages them to pee and pass any toxins that have built up.