If you were giving the injection into the arm, it would make sense, but having pain in the arm when you are injecting your stomach is a little weird. Is there pain all the way up from the injection site to your arm, just pain in your arm and not your stomach or pain at the injection site, no pain in between and then a pain in the arm?
It might be normal, but I think I'd ask my Dr. if I were you.
sam1234