C.H.
Ok so here is my experience: my kids had this 2-3 times per week for about 6 months. It turned out to be a milk protein & egg allergy. I would definitely get them allergy tested (they can do it by simple blood work).
This sounds more like what my good friend went through & it was kidney related. I would recommend looking into this as well...she really had to push her doctor, but it turned out she was right.
Hopefully it is just allergies.