Need help. 12 weeks postpartum complications.

So I tore a little , got stitched, after a few weeks felt much better. Then suddenly I had a wound like area around the site of my tear and it stung every time I peed cause urine would get on it.

I went to the dr and he put this medicine/acid stuff on it and it killed it and turned it gray. He said it’s because it’s so wet down there the wound couldn’t scab and heal. Well ever since he applied that acid medicine it’s way way worse. Like around the whole opening of my vagina is basically just one open wound and god that acid hurt soooooo bad I don’t wanna go get it again... I can’t find a single thing about this online anywhere. I have no clue what is going on.. :(