I have a rash on one of my arms and I've had it for 2 days. Its a bunch of small red bumps and it feels like its on fire when I itch it.

Red vesicular rash. 18 year old with painful burning vesicles on arm. Get a full medical history and in person physical exam ASAP. You can try a consult in your area as well. If the rash is itchy (pruritic) and painful you need to give more history. The differential is large and it could be anything from zoster to contact dermatitis to chiggers or a reaction to insect bites, bedbugs, or scabies. A picture=1k words.

Related Questions

I have small red bumps no itching all over my arms what could it be?

Many things. It could be simple things such as a folliculitis or keratosis pilaris, both of which are benign conditions. It would be useful to know how long they have been there and what they look like. Read more...
KP? Keratosis pilaris probably. Try daily exfoliation and then gentle moisturizer without dyes or scents. Read more...