We were told not to use motrin until she was older. I think six months. Anyways just keep him a comfortable as you can. I think it like 2days or so with a temp and you call the doctor. I don't remember if it suppose to be so high or not. My DD ran a low grade fevers too after her shots. Also as long as the are where he got the shot are not rasied and feel hot then he should be fine. If you are worried then i would call your ped and see what they say. My ped usually gave us a paper with what they could take, the dosages for that age, and when to call them with concerns.