Perhaps you are putting too much on the area, BP can be harsh for some. I use Differin each night and thought if I put a dab of BP on a problem area (side of chin) it would double attack it. Well....I burnt the skin, red, swollen, and cracking. bad bad....now I just use the Differin and then apply a good cream over it.
The chin is a big problem for many women, apparently it's hormonal which makes it very hard to keep under control.
I'd give the derm another shot with something that isn't so harsh and keeping the skin well moisturized. Perhaps antibiotics? I'm also using Minocycline and it seems to be working well in combination with the Differin.