Toddler rash and almost black poop

WARNING: HAS A BABY POOP PICTURE

I made a post yesterday about my almost 2 year old son having a cluster rash on his back (He is up to date with vaccinations). The rash has now spread to his stomach. And for the past 3 days I've noticed he's had grainy black poop. Today is the first day it's solid, but it still looks dark with tints of red, so I'm not sure if it's normal. He hasn't ate anything red in color. He also won't eat. I've been calling his doctor all morning to try to make an appointment but they aren't answering 😫 Just want to get some more opinions while I wait on them to answer lol Help a worried momma calm herself 😢