Is there still a chance I could be pregnant

Patient: My last period was on dec.15 2013. I took a pregnancy test on jan. 26 and it turned out negative. It is now feb 7 and I still haven’t had my period. I’ve had sex a number of times between dec 15 to feb 7. Is there a chance I am pregnant even though my last test was negative. Over the past yr my periods have been so irregular. I’ve been trying to get pregnant but because my periods are so irregular it’s been difficult to track my ovulation days.