Birth control

I've been on the same type of birth control pill for about 2-3 years and have never had a problem with it, I've never had any cramping on my time of the month or anything. I was never on it for pregnancy issues mainly for health issues(period lasting longer than a week and causing me to be sick becuase I was anemic) but since August I've been using it for preventive pregnancy and I've noticed I've been getting severe cramping, the week before my period and severe headaches the week before. I know some people who have had to change their birth control becuase they have had problems but with me being on it this long I though it was fine. Is this a birth control problem or could it be something else?