what could be causing constant itching on the back of my neck. It has been going on for several months. There is no rash, just itches in the same spot

Hello. Thank you for posting.

Causes of itching are numerous and can include insect bites, allergies, and infections.  It could also be as simple as a tag rubbing on the same spot over and over from a shirt or coat you wear often, causing irritation. If there is no rash, bumps or sores, it might be systemic.  We cannot know. I would mention this to your doctor as it's been going on a few months. 

Helena