Birth control: Is it possible to not know you're pregnant?

I have been experiencing symptoms of pregnancy a lot the last week or so. I have gained 6 lbs in a month and until the last week, week and a half I haven't eaten a lot more. But this passed week or so I have had a HUGE increase in appetite and cravings, extreme fatigue, mood swings etc. For a while I have attributed this to the extra hormones of the patch but the women I have spoken to say they never experienced these things, mostly upset stomache which is something I have not felt. Should I consider a pregnancy test or is that foolish? We DID have unprotected sex a few times before I began the birth control but the pregnancy test was negative. Is it possible I got pregnant then started birth control. I thought that if that were the case a birth control would stop the pregnancy. Not that I would want that but I am very confused at the possibilites.