Try taking out the most comon allergens first (dairy, egg, wheat, soy, fish, shellfish, peanuts treenuts) theen add them back iin one by one. I'm just not sure abbout tthe timeline though. Try posing the question at kidswithfoodalleries.org and you might get more answers. I knew something was up with my son while he wwas exclusively breastfeeding, but didn't pinpoint what until hhe started solids. Turns out he was allergic to four out of the list above plus one more (sesame, whisch is also getting to be a common one). Good luck!