Could I be pregnant even though my test came back negative?

Patient: I just got off birth control except while I was on it i missed a couple pills and still had sex without a condom. I have experienced symptoms such as nausea, throwing up, mood swings and pain in my breasts and since then have had such light and irregular periods that i think it is spotting, however i got a pregnancy test last month and it was negative. could i still be pregnant?