Hi, Had he taken any food items other than usual? Any history of atopy, like eczema or wheezing in the past? Welts indicates some form of allergic reaction, which may be associated with vomiting if there is mucosal involvement too. Many times we will not find out any specific cause. If he is otherwise active and playful, and not associated with breathing difficulty / stridor / swelling around lips and eyes, you can give antihistamine like hydroxyzine for 5 days and ondansetron for 2-3 days, both three times a day (dose depends on age and weight). Calamine lotion application over welts can have a soothing effect. If not getting down in 2 days or the above said features are present, kindly take him to doctor as he may need steroids too. Meanwhile give frequent feeds in small amount, to improve retention. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Muhammed Aslam T. K., Pediatrician