Mostly water poops + white pimple bumps

My exclusively breastfeed 2 month old son has been passing extremely watery poops for a while now it used to be a bit creamy but not anymore. No seeds or nothing. It also just explodes out of his poor bum sometimes, leaving me stuck with yet again another diaper rash. Last one stuck around for a month with nystatin treatment. This time the rash isn't too bad but it's accompanied by white pimples on the crease next to his junk on each side. I've started to give him lots of nakey time. I still have the nystatin so I'm treating them both with that but wondering why his poops are so terrible.