Black flecks in poop

DD is 10 weeks and EBF. About two weeks ago I noticed these black/maroonish flecks in her diaper. She also had some diapers that looked mucousy. It lasted for about a week and then went away. We brought in a diaper with the black for her Dr to see at her 2 month appt and he didn't seem that concerned. He said it looked like blood but was one of those baby things that would resolve. After that her diapers looked normal but now they have black in them again.

Anyone have experience with this? I eat a good amount of dairy, which I read could cause this, but I don't feel like the amount I eat varies that much so I don't know why the black flecks would come and go. DD doesn't seem to be in pain or anything. She's a fussy baby and tends to cry a lot but I can usually get her calmed down relatively quickly. She never spits up and doesn't seem any gassier than any other baby. Thanks for your help!