Headaches just before and during periods is the result of Hormonal activity and are often called as Hormonal headaches. It happens with 60% of the women. The main trigger of these hormonal headaches are oral contraceptives and since you have mentioned that you use one, it explains all. It can be treated in a number of ways. The best way is use of an Nonsteroidal anti-inflammtory agent like Nalfon, Relafon etc. Here is a link for complete details:
Headache
Headache