Not an allergy, but some kind of intolerance?
Essentially when she was a baby she was mix fed. When bf she would spit a bit back up. But when ff she would throw it all up. We switched to a 'hungry baby' type at 2wks and she stopped being so sick.
Since we switched her to cow's milk at 1yo she has had lots of issues with poo, toddler diarrhea, then longer between poos, but lots of poo accidents after potty training. Poo soft, so not constipated exactly but treated medically as such.
Decided as last resort to cut out dairy, was using soya products then cut those as well and used rice milk. It didn't seem to make a big difference so allowed her to eat dairy again (after 3wks). But only small amounts, as she doesn't eat yoghurt or much cheese, and we had loads of rice milk so she kept drinking that.
Ran out of rice milk. A few days later she started having poo accidents. Gave her rice milk again.