I have an unusual crawling sensation beneath the skin on my back at the left shoulder, usually on the same spot. what could be the cause?

Notalgia paresthetic: Notalgia paresthetica is an itchy spot usually in the infra scapular area that is actually due to arthritis in the vertebral column of the back. It is due to inflammation of the sensory nerves that exit the foramen which is then interpreted by the brain as itch. This leads to chronic scratching which leads to a thickened plaque of skin called lichenification. Try taking Ibuprofen or acetaminophen.