I am worried about my puppy?

a few weeks back my dog had brown spots on his stomach and I took him to the vet. The vet said that he has eczema and that with the special shampoo he gave me (which consisted of mostly Selsun Blue) and a steroid shot, my puppy would be fine. I gave him the bath and he was fine for up until about a week and a half ago. The brown spots reappeared on his back and he is biting off all of his fur on his right back side and now on his tail. The vet said when I was in last time that the marks looked like signs of mange, but it wasn't.I gave him his bath on Sunday again and it doesn't look like it's clearing up. Do you think he could have mange, or can it still be the eczema?