It is horrible to have to watch them be inthat kind of pain. If you haven’t had the vet, I too would highly recommend it.
My horse had the same issue, I panicked and hauled him three hours to a vet in CA. I thought he had damaged a suspensory. Was throwing his front leg up in the air and grimmacing with the pain. Vet did a block, pulled the shoe, and found the site, drained it and a few weeks of layup he was good as new.
If you can’t see the exact site, you can soak in warm water and Epsom salts for about 30 minutes then pack the hoof cavity with Ichthamol, nasty smelling goop. Cover it with gauze or cotton and totally vet wrap and duck tape it. You can leave this wrap on for a couple of days, then do over. It is meant to draw the pressure from the hoof area.
I have also done this on two other occasions, different hoof, with the same horse. Soundness returned, but the next shoeing the farrier could see a bruised, blackened area when he pared the sole. It just never manifested to a draining abcess.
Hang in there, and do all you can for the horse.