Left side , back of head pain when laughing, bending over and coughing. what could cause this?

Tension headache: It seems that a muscle that runs from the back of your head to the neck on the left side is tight causing muscle tension headache, especially when you perform the activities you mentioned. Applying heat or at times ice might help. Stretching exercises to relieve tension will help along with medicines like ibuprofen or naproxen . Please go see a doctor if not better after doing this for a week.