I would love some help troubleshooting here, because some major signs are pointing to milk allergy, but I'm not totally convinced. This is long, sorry!

My LO is 4 months. My first was mspi, so i limited most dairy from his birth (but didn't worry about things cooked with butter if i ate out, or look at ingredient lists, just the obvious). At 3.5 months, i had a little of a pasta dish with cheese for dinner, and the next morning he was uncomfortable all morning and then had 2 bloody poops, the first little black flecks and then a little later, bright red streaks. It was more dairy than i usually have, but not a ton. he was fine after that.

Fast forward 10 days and we introduced 2 oz of formula for the first time - milk based. He did great! But my older kid had the flu so we held off on giving it again in case he caught it. So now it's been a week, and on new years, i had a few little pieces of cheese, and a piece of cake that had butter in it. I also ate something for lunch yesterday that made me very sick. I felt kinda sick all night too.

This morning, he was cranky, and i feel a tooth popping through. Gave him a cold teething thing to chew on and he felt much better. He's been a little congested and coughing, presumably from the saliva (sooo much drool!) Then suddenly the same bearing down, followed by a bloody mucousy poop.

Soooo, what gives? It seems like he has the mspi symptoms, except he did great when he got a little milk formula directly, which makes no sense! How could he react so immediately to small amounts in my diet but not to formula? Or could this be something else? Should we try formula again? Can you get bloody poop from teething? The mucous could definitely be from that.

Am i just in denial? I really want to get him on formula and don't want to have to get the special stuff unless we have to! But I don't know what else this could be. Maybe another food other than milk?