Hey there! It's been a year, but I'm back to update this thread incase this could help another person. It turns out you and your friend were right lioness, it was indeed due to a damaged nerve in the back of my neck!

My posture at my work desk for the past 3 years had been horrible (screen to the left, so head always looking to the left), so I ended up fixing my computer set up, have incorporated a schedule of getting up and stretching and massaging certain areas throughout the day, and occasionally go to a massage therapist, and I'm at a point now where the headaches and jaw pain have been a thing of the past since autumn last year!

I still get the occasional small sharp pains in the right side of my head, but it's mostly just a warning that tells me whenever I haven't been massaging enough, and it goes away with enough care.

Thank you so much for the tip, lioness!