T.H.
That is odd. Have you been giving him any foods? Could it be a reaction to a new food or his formula? Does he have any other symptoms? To me it also seems unlikely that he would be getting a virus each week...he has just done it once/week? I would maybe start charting exactly how much he's eating and when he eats to see if there are any patterns. If you have given him any new foods stop giving them to him and then reintroduce them slowly and one at a time. If it continues and you see no other symptoms, etc. I would maybe get a second opinion.