How did you know baby had milk protein allergy?

[butterfly_tx_22]

Our first daughter who is almost 3 had a milk protein allergy...at least that's what I believe. When she was a few weeks old she started getting mucus in her stools and from as early on as I can remember was a very fussy baby. She always seemed to have tummy issues and her ped. didn't feel like it was a milk protein allergy, but I stopped eating dairy and she got much better. By 5 months of age though I just couldn't handle breastfeeding anymore and she was put on Similac Alimentum and did well with it. I now have a one week old baby girl who is showing similar signs to what our first daughter showed. Very fussy, squirmy, and mucus in the stool already. I'm so upset...I'm cutting out dairy from my diet starting NOW and hoping that will help. What kind of foods did you eat and did you avoid all dairy? Anyone use Alimentum at this young age? I feel like if she doesn't get better I want to switch her to that formula.