Itchy boy is making himself bald

Hi folks, I need advice on my BC’s skin issues. He’s been having issues since August of this year. Over the summer I think he got fleas from our cat, and he seemed to have a reaction to them. He developed a reddish bald spot/sore above his tailbone , and was constantly biting and licking that spot and it got bigger and bigger. We assumed he got fleas from the cat, so treated him for fleas. Vet couldn’t confirm if he had fleas or not because we had already treated him. He kept itching. Vet prescribed him prednisone (steroids) and that helped. Tapered him off the steroids and bald patches/ itching his groin, base of tail, and armpits returned. We put him on steroids again. It got better and we tapered him off steroids again. The itch is back and he’s licked himself bald around his anal/groin/ lower belly area. The skin is reddish and leathery looking. It’s spreading and I am not sure why this itch has continued for so long, what the root cause is, and what to do about it. Additionally, his nose has turned crusty around the edges. I’m assuming it’s a flea allergy that triggered this. But maybe I’m totally wrong. Has anyone dealt with this before? I am going to take him to the vet ASAP, but wanted to see if I can get some ideas in the meantime.