background- my LO is 4 weeks old and I've been exclusively pumping with the occasional random nursing thrown in since we left the hospital.

in the last 4 days, her poops went from mustard yellow to progressively greener and slimy with mucus and she got fussier and gassy. At first I thought it could be a foremilk / hindmilk and/or overfeeding issue because she was drinking bottles FAST and I have been engorged too much lately due to missing pumps (toddler!)
but still pumped more than enough easily for her.

THEN, I wondered about a food allergy or intolerance, as my son has food allergies.

Based on that (here's where I majorly F-ed up) I thought I would try formula (normal milk based Honest Company) for a day and see what happened. (I didn't really think it could be a dairy issue, I was thinking about my son's allergies to wheat and nuts)....

What happened is she still feels bad, is sleeping less than ever and crying more than ever, and her diapers are green and mucousy AND have streaks of blood in the mucus now and some huge chunks, almost like chewing gum (milk solids?).

Does this sound like MSPI to you? When she was getting breastmilk I was having a tiny bit of dairy - like on cereal and in coffee.....but obviously the formula is like "hi, here's a ton of milk"........

Just stressing now and waiting for morning so I can take her (and the weirdest grossest diaper ever) to the pediatrician.