Baby rash?! Help!

Does this look like heat rash or a diaper that’s too small or a yeast infection? I already made an appointment with his pediatrician for first thing in the morning, but i feel so bad for him because this looks so painful. i just want to know what is going on. we change him obsessively, and everything in our home is fragrance free. we live in arizona, so it is very hot, and heat rashes are pretty common, so that came to mind. the swelling was pretty bad, so i gave him a sponge bath and have been airing out the area and it’s gone down a little. it doesn’t bother him when i press on it or anything. it goes down to his butt as well. has anyone seen anything like this? how do

i make him comfortable until the morning?