What Causes A Delayed Period With Negative HPT?

I am 9 dpo, 5 days before my expected period. Normally I have a 28-32 day cycle but this month it has been off. This is the first month is a while that I am off my bc. I ovulated 3 weeks after my last period (1/16/09), and had intercourse 4 and 2 days before ovulation and the day after. I feel sick, nasua, headaches, stomach discomfort and leg pains. I had cramps last week, but not anymore. Plus after ovulation (2/6/09)I didn't have any vaginal discharge up until yesterday. I took a hpt today and it was negative. Could I be pregnant?