Dark stool

Tasmina • Can't wait to meet my baby boy in April 😍
My 10month old has a really bad cold for last two days , severe congestion. He  has been miserable but seem to be feeling better. He normally eats purred veggie , chicken , rice etc. but because of his cold he was only having rice cereal with formula and breastmilk ( much less because of congestion). Today he pooped after two days and it caught me by surprise. It was really dark , almost black and very dry. He has done this same poop about a week ago but then it was normal . I am waiting for the doctor to call me back but in the meantime please let me know if you have any experience like this with your baby. Google isn't helping but making me more anxious. Please help! Thank you