What could be the cause of this?

Off and on headache since last Friday. I have been drinking a lot of caffeine during that time period. The headache is always centered near my scalp line, left of center. It’s maybe there for 40–50% of my day. It tends to appear if I am really stressed, but can do so at other random times.

My job stress is getting worse and worse. I’ve been sleeping horribly too (although the caffeine is no doubt not helping…