Measure your blood pressure. If it's low — half a tablet of Citramon or a cup of weak coffee. If it's high — half a tablet of papaverine or No-Spa. Try to resort to medication only when you really can't bear it anymore. Try mint tea, a wet towel on your forehead, and sleep more often. I also suffered from very severe headaches at this stage; it's the leftovers of morning sickness, there's nothing you can do about it.