Skin on Left forearm and upper part by shoulder sensitive to touch. It has a burning sensation even when not touched. Not red no rash What could it be?

Nerve irritation? Sounds like a nerve could be irritated. My main concern is if this could be an early sign of shingles. Sometimes there will be pain before the clustered blisters show up. Shingles affect a cutaneous nerve on one side of body, so pain and blisters usually extend from spine to midline on front of body. Any nerve, from head-to-toe col be affected. If blisters develop, I'd see a doc ASAP for antiviral.