Y.D.
Jennifer has given great advice as well as everyone here so there is not much I can add. I am not a huge proponent of all vaccinations, while most are good some are not needed, e.g. varicella vaccination but that is just my opinion. Make sure to keep detailed notes during his adverse reaction to this specific shot (and any others for that matter) and make sure his pediatrician notates what you have detailed in your son's medical records for legal purposed -- if needed. Every vaccination my daughter has received I demanded that I get the serial number and the manufacturer for record keeping just in case.
Like many others have suggested delaying his vaccination schedule may be best for your child. Children's immune systems are very green to these shots sometimes so parents must be aware of the stuff they put in them. One size does not fit all if you understand what I mean. I fought tooth and nail to seperate my daughter's MMR shot. To this day she still has not had her measles shot because she is not in daycare nor preschool so there was no need for her to get it at the scheduled immunizations that is dictated by the government. And if your pediatrician does not agree delaying your son's schedule find another pediatrician who will listen and understand what you want as a parent. Parent's have lost too many rights when it comes how to raise our children and what we feel is best for them.
Best of luck and God Bless.