Hello, That is not typical of the usual pattern of viral infection in kids. Of course it could be, kids do get 4-6 infections, some would say even 10/year. The first thing I d suggest is that you write his symptoms when they occur on a calendar so you and your pediatrician can see if there is a pattern. But, if it the symptoms are really reliable, and really spaced at exactly 4 weeks, then I would take him to see his pediatrician. More questions needs to be asked and answered. Although unusual, there are migraine patterns that could cause this, including abdominal migraines. There are some periodic fever syndromes, such as Familial Mediterrean Fever, or cyclic neutropenia (low white blood cells) that could account for this. And finally, I would always consider stress and anxiety as a reason. For 3-4 year olds, this is a big time for normal separation anxiety - consciously or not. Children in general often have more physical signs and symptoms of stress. Hope I have answered your query. Let me know if I can assist you further. Take care Regards, Dr. Lisa Baker