Sounds like an allergy to me, just a grandma, but not necessarily to the tetanus part of the shot. I'll bet you are sensitive to one of the non-active ingredients. It could be the aluminum adjuvant, thimerosol or formaldehyde. You can look up vaccines at http://wiki.medpedia.com/Vaccine_ingredients_-_sorted_by_vaccine
I watch out for vaccines that contain gelatin and sulfite preservatives because I get nasty reactions. I take Benadryl when I get reactions, but you should call your doctor first!