Hi muffetbane, the symptoms you describe sound like it may be Metabolic Bone Disease or MBD. Here's a link to a PDF of an article you should read asap and consider examination by a veterinarian for an authoritative medical diagnosis and treatment.
https://lafeber.com/vet/wp-content/u...BD-Handout.pdf It's most common in Reptiles and Birds but it is a not-uncommon malady in amphibians as well. Also looking at your photo, it appears that your little Poliwag is very slightly structurally malformed which is also an indicator of MBD as they get to be about this age. Poliwag has the markings of an Anaxyrus americanus americanus/Anaxyrus americanus fowleri Hybrid. These naturally occurring hybridizations can also bring greater risks of MBD and other maladies, but they are treatable and if treated soon enough the afflicted individuals can still have a long happy life as a pet. I'd appreciate it if you'd PM me with any updates on Poliwag's condition and progress.
KP
PS: On the skin issue, it is shedding in progress but the possibility of MBD if it is present will make shedding very difficult for Poliwag which is why it seems like it's taking a long time and not working very well.