Milk Allergy?

Zoey

I am breastfeeding and lately my daughters poops have been brown and mucusy. Occasionally she’ll have a green/yellow seedy poop and then it goes back to the brown poop. She’s not constantly pooping so I know it’s not diarrhea. I thought it was protein shakes I was drinking so I cut those out and her poops haven’t changed. How did you know if your breastfed baby had a milk allergy??