Not a life threatening allergic reaction in my opinion, it should go down. More of a concern would be if it is infection because of the non-steralized injection the girl gave you... sweat, dirt, etc at the puncture site. Is the redness general or is it a streaking line down the arm? If it appears to be infection, then head for the doc's office. If it is more just swelling and redness due to allergic reaction, then just continue what you are doing.
When one tugs at a single thing in nature, he finds it attached to the rest of the world. John Muir