Okay i got some pics uploaded of the rash
http://img842.imageshack.us/i/001xc.jpg/
http://img826.imageshack.us/i/002i.jpg/
A rash on the arm is not a STD symptom. A rash within 1 or 2 days is not a STD symptom. See a Dr, this is not STD related.
I have moved this over to the Dermatology thread so you can further advise of your rash condition being that it does not appear to be STD related.