More baby poop. Black /: 💩

Hi everyone. We brought my son to the doctor today because he was running a fever. There was no fever at the doctors office and behaviorally he is just fine. The doctor said he look like he was in great shape and had no concerns. Since that trip this morning, he has had the diarrhea multiple times and now there is black in his store. He is exclusively breast-fed and usually has yellow poop. I posted last night a picture of it, and at that time it was green.

I’m pretty concerned! I can’t get ahold of the doctor or his nurse. Would you take baby to ER?