Okay ... well, at least this gives you a place to "vent?"
And, as you say, there is no answer ... at least nothing any of us can provide (or the two dermatologists you consulted).
But check back in a year because, in my opinion, your problem will have resolved. Until then, try not focusing on the PIH, because other people do not notice it (they are too worried about their own faults).
Trust me, a few "dings" here-and-there will not ruin your life ... unless you think it will. I'm so covered with dings, scars and barnacles I look like an old Grey Whale. Physically I'm a mess ... but I usually wake up in the morning with a smile and willingness to forge ahead (after a cup of coffee), thru all the aches and pains and body falling apart. I helps if you stop looking in the mirror. Picasso did it when he got old and mangled ... and it worked!