You should definitely go see your primary care doctor
about this issue right away! They can evaluate your rash and your pain and figure out what might be going on.
The combination of rash on the skin together with burning pain in the same area immediately suggest shingles to me. This is a condition caused by the same virus that causes chicken pox. Basically what happens is that after a case of chicken pox the virus is never completely eliminated from the body. Rather, it hibernates and then reactivates, usually during a time of great stress or illness
. The reactivation causes both a very classic rash limited to one part of the body and burning nerve pain in the same area as the rash.
If the rash doesn't look like shingles, your doctor will also consider other potential causes, include the possibility that the pain and rash are not related to each other at all but are, rather, two totally separate conditions. For example, you could have an inflammation of one of the nerves in your arm from an overuse injury, causing the pain, and simultaneously a case of bad eczema
or contact dermatitis causing the rash.
Talk to your doctor!