Last month, I missed two birth control pills and had to start a new pack (as instructions said to). A week after starting the new pack, I had sex with my boyfriend. I had withdrawal bleeding (or what I believe to be withdrawal bleeding) from the time I missed the pills until a day before I was supposed to start the placebo pills and my period. My period came, lasted five days, and then I started my new birth control pack for this month. However, now I have extreme nausea, I am very tired, and I have minor headaches. I took a pregnancy test yesterday, but it came up negative. So my question is, could this be a result of me messing up last month's birth control or could I be pregnant?