Sorry about the lack of comments, Bob
To me it looks like a bacterial infection. I would suggest picking up some baytril, bactine, reptiboost, and unflavoured pedialyte. I would then give her a pedialyte soak of 9/10 dechlorinated water, 1/10 unflavoured pedialyte, along with 3 drops of natural honey to give him some energy.
Before giving him the pedialyte soak, I would move him into a 5 gallon tank with moist paper towel for substrate and an easily accessible water dish, as well as a black background to help the frog feel more secure. Refresh the substrate daily, as well as the water in the water dish (I am currently having to forcefeed my lethargic Green frog (Rana Clamitans), of whom is only 3 inches head to vent, so I can advise you on how to forcefeed a small bullfrog/green frog.)
How weak is the frog? I would place crickets in his tank (you can take off the hind legs so the frog can catch them easier) or chunks of earthworms, and wait to see if he goes after them. If he doesn't you may have to forcefeed him, but I'm not sure if you can with that abcess on his lip, and his tiny size.
More photo's would help a lot.
I advise a vet for this frog, that looks like an infection to me.