How can I get rid of neck pain?

The right side of my neck has been hurting for a few days—specifically, right about where my neck meets my shoulder. I’ve also been having some headaches on and off that seem to be related to this.

Any ideas on fixing this? For what it’s worth, I don’t think it has anything to do with sleeping funny—I made sure to sleep on my back last night, and I woke up feeling fine; my neck started hurting a few hours later.