Two cycles ago, I did a bunch of site injections with Anatest Propionate and ended up looking like the Elephant Man. I had nasty bruising and swelling, the pain was beyond description. I was pretty scared and ended up visiting the Doctor and told her what I had done. She said the lack of a fever, coupled with the exact same injury at every injection site, led her to believe that an infection was not involved. No antibiotics were prescribed. Several days later I began to recover and everything went back to normal. During that cycle, I was also using Cytadren, which resulted in a massive delay in my clotting times. That would explain the bruising that I had.
In my opinion, I think what you've got is a garden variety reaction to Prop. Most guys experience some swelling and pain with Prop shots. It'll last for a few days too. If you're comfortable around Doctors, drop in and tell'em ya did B12, see what they say. If not, wait a few days and see how it goes.
I love Propionate, its one of my faves. Prop and Sustenon is all I run for Test. But after that experience, I only use it with glutes. Leave the site injections to V and Fina.
Peace,
S.