Just a thought, but if you have insurance you could go to the doc. Just tell them you did a b12 shot. I did that when i had an infection and I doubt the doc bought my story, but I was treated and glad for it. If you can notice that is it hot to the touch, or noticeably warmer, I'd recommend seeing a doc, better safe than sorry. Oh I did what you did, guessing for about 5 days or so and then I sucked it up and stuck a pin in my delt and drew back to see some pus in the syringe, went right to the ER from there.