I've been taking prometrium vaginally twice daily for 13 days now (started the day after my IUI) and on day 10, I started noticing a headache, a dull gnawing sensation on both sides of my head. It is day 14 of prometrium now (CD32) and I am still feeling this. If I bend over to pick up something it hurts even more. I haven't taken anything for the headache yet, but I've heard that when you are pregnant, your blood vessels dilate and I wonder if my headache is related to prometrium or possible pregnancy. When I first started prometrium, I was exhausted, but I got over that in 2 days. Since then, I've had no side effects except for these headaches. Has anyone experienced this before?