My suboccipital muscles behind my head are tender to press and have been for weeks. ive had a ct scan and no adnormalities. what could this be?

Tension: Muscle tension can be caused by some chronic stress or poor posture habits at work,in bed, watching tv,etc. If no abnormalities were detected in your vertebrae and no abnormal curvature of the cervical spine, a trial if muscle relaxant, massage therapy or stress management therapy may be helpful

Headache : You are describing a suboccipital muscular, tension headache. This is treated with the typical remedies which include heat therapy, massage, and anti-inflammatories. You should check with your primary doctor or possibly a neurologist to confirm that this is the problem.