It's always a possibility, and best to be on the safe side. I never really got headaches until I got on prenatal vitamins. Every woman's body reacts differently, apparently, so I can't say anything. I never really got too sick- once again, until prenatal vitamins- so you never know. As for cramps, make sure they're light. If not, then that could be a symptom of an early miscarriage. Most miscarriages happen before you even realize that you're pregnant! Keep updated and I'm here if you need to talk.
Also, birth control can be easily unconcentrated. What I mean is that my ex-boyfriend's mom got pregnant and she was on birth control. It was because of an allergy shot that she had gotten that diluted the effects of the pill.