What Causes Headache With Pain In Eyes?

I am 38 and delivered my third child naturally 4 weeks ago. I am experiencing intense headaches every evening. They start on the sides of head then shortly after they begin I have a lot of pain in my eyes and then on the top of my head. It does subside to a much more tolerable level after taking Tylenol, however the headaches seem to be starting earlier and earlier as the weeks go on. What could be causing this?