Hi and welcome to HCM. This can be pyloric stenosis but it would start at 2nd week of life. It is possible that symptoms werent noticed before. I think that further tests are neccessary to evaluet intesitnes passage. Contrast radiological imaging could demonstrate any kind of stenosis,stricture or atresia. It can be found in esophagus, stomach or small intestines. It is most imprtant that she develops and grow normally. Food allergy wouldnt manifest on this way,but it can be considered if there is no organic pathology. Wish you good health.