Sore skin on arm no other symptoms. 20 yr old female. had a flu shot 2 weeks ago but feel fine otherwise.

Umm, hard to say.: There is nothing specific about the skin you describe that gives us a clue as to what exactly is going on medically. Does the rash go away--or is it persistent? Is the skin itchy?... Is it smooth or rough? Does it get worse or change colors after a hot shower?...As you can see, there are too many questions unanswered; however, taking a wild guess this may be post-injection neuralgia. Ask your md.