Poops!

My 15 wk old is exclusively formula fed. Most of the times when she poops it’s over night so I don’t get a good look at it. When I last changed her poopy diaper last weekend during the day it was a lot thicker than normal… I had to scrape it out from being stuck between her cheeks. Nothing in her diet has changed. The baby sitter today said it was black (then said it could have been it’s normal dark green color, it was 4 hours after she pooped that she remembered to tell me) and that it was not her normal stinky formula poop smell and thick and tar like …can anyone think of why it would be a different consistency if nothing in the diet is different?

*I did call her pediatrician…they told me to monitor it and if she has a black tarry type of poo again to make an appointment.