What Causes Headaches After Falling Hard On Buttocks?

Hi, I recently had a hard fall while rollerskating. I fell on quite hard on my butt, and from the next day on until now I've had a heachache in the right side of my head. It's been 5 days and it's still there. It's not debilating, but more a dull headache which is annoying. WHat can I do about this? Thanks.