My 4 month old went from pooping once a day to 5-6 times a day and when she does it’s watery with these chunks. Or just watery black consistency m.

We don’t ebf and give her formula. My s/o also said while I was working her poop was mucusy with a foul odor. One of her diapers were black and sticky/slimy. We haven’t done anything different.

What could be wrong? I called nurse and she says it’s an infection but could babies fight it off okay? I was going to go to the doctor if it didn’t get better by the end of the week