Hi there, Thank you for choosing healthcaremagic. I would like to ask you some questions before I am able to point you to the right direction. How is your son s diet like. Apart from soy formula, what else does he eat, and what is a typical daily routine for his diet. How are his stools like- soft/hard? How frequent does he have his bowel movements? What does his vomiting look like- is it green in color and does it have food particles in it. If your son has been gaining adequate weight and he has no fever, and otherwise is doing well, then he is probably alright. It may be that he may have eaten something that doesn t suit him or some dairy product that you may not be aware of since he is allergic to milk protein. Also, if he has a history of constipation then that maybe a reason for his occassional vomiting episodes and in that case he needs good amount of fiber in his diet as well as plenty of fluids. In case he is having severe abdominal pain, problems in weight gain or his vomiting is getting more frequent, then he needs to be seen by his pediatrician to have a complete evaluation of his vomiting. Hope this helps. Best wishes, Regards, Dr. Sumeet.