Left side base of skull pressure headaches?

I too experienced base of the skull pain/headache that eventually effected my shoulder, back and front. Mine comes from clenching my teeth at night, really bad! I woke up one night in so much pain in this area and caught myself all clenched up. I was amazed! I took muscle relaxers (Flexeril) every 6 hours, for 3 days in a row and it relaxed everything enough to settle it down. I do have TMD and this must be another manifestation of how bad it can get. Check with your dentist or oral pain specialist to have it checked out...and get some muscle relaxers to break the pain cycle! Good luck!