I have a red bump on the back of my arm it hurts to touch it. It also has a area of red irritation around it. I thought it was a pimple but hasn't come to a head in the last couple days so now I'm thinking maybe its either a boil or spider bite. Should I go to the hospital for it or just wait it out?

If it has a red area around it there could be an infection. The hospital might be excessive, but might be worth calling your doctor or going to urgent care.

Could be a spider bite. Have you been in a tick area? Does it look like a bullseye? That could signal lyme disease from a tic - in which case you need to get antibiotics ASAP because that could make you very sick. I had something like this at one time that continued to spread and turned out to be shingles - not fun. Your spider bite guess is probably accurate though.