The lower, center of the back of my head feels like there's an injury (long cut) and burns, but there's nothing topical. what could this be?

Possible shingles: If only on one side of head it could be shingles from prior chicken pox.This commonly presents as an uncomfortable skin sensation before the rash shows. The issue is not the rash, which clears rather quickly, but rather that you can develop pain that lingers- post herpetic neuralgia. See your MD for evaluation so you can start appropriate medication early if needed and avoid long term problems.