I'm too new to answer most your questions, but if you post an image of the frog it might help other assess his health/the bumps. It's good you found out about the mealworms, at most use them as an occasional treat if at all.
Don't take earthworms from your yard! They can contain toxins of all sorts and parasites! Even if your yard is pesticide free you don't know where else they've been or what metals or whatever else they've been exposed too. However if your local petstores don't sell worms you can get them from fishing supplies stores or even walmart, just be careful that you don't buy the ones that have been dyed or scented, and you want nightcrawlers, redwigglers have nasty smelling juice that could put you frog off worms forever if he's picky enough. If he's small you may have to cut the worms into thirds/in half. Crickets will be a fine staple as long as you're gutloading and dusting them properly. Earthworms would be a better staple though, especially if he's struggled to grow on mealworms, they're very high in calcium.
You might try offering freshly molted (white) dubias, mine didn't eat them at first either, I think she hated the texture of their shell, but squishy molted ones did the trick eventually.

Glad he's eating well! How old was he when you got him? What size is he now?