Getting shots doesn’t bother me. I wish I knew my secret so that I could share them with the world, but alas I do not. Even the dreaded anthrax vaccine ( which everyone says hurts alot) didn’t hurt for me. When we got 5 shots in a day in basic training, everyone but me had bruised arms. ( and no, Tetanus didn’t hurt for me either)
Some wild speculation:
I take quite a few vitamins, including C, E, chromium, multivitamin, co-enzyme Q-10, Lutein and Lycopine. If it’s one of these, it’s likely to be one of the first three, since I was taking them before I went to basic training. Vitamin C is an antihistamine IIRC, so that is a good candidate.
Another theory of mine is that I just managed not to move when they used the autoinjectors on me, while everyone else moved, thus getting injured. Though this wouldn’t explain regular injections.