Well, generally speaking, the headache is normal after you have taken the prk surgery. According to some researches, headache can be caused by some reasons, such as the eye strain. And you should know that if you have taken eye surgery, your eyes will be sensitive. So if you overuse your eyes, it will lead to high eye pressure and eye strain. In that way, it can put stress on the eye muscles and the facial and scalp muscles. In some cases, it will affect your brain nerve system. In that way, it causes pain and headache. After the surgery, you are not supposed to take some heavy exercises, or it can be dangerous to your eyes, making your headache worse. For your situation, you can use some eye drops on your eyes.