Light period + negative test. could i still be pregnant?

I had unprotected 2 days before ovulation (and I know when i ovulate because i get sharp cramps for several hours). Well, I had my "period" a week ago. I started on time, but it only lasted about a day. I spotted for a few hours, then stopped till later that night where I had enough "flow" to fill one tampon and then stopped again. I'm normally a regular 3-5 day girl so I thought it was kinda strange. But I took three different tests afterward (two days after period) and they were all negative. So I guess I'm not pregnant... or could I be? I've been ridiculously tired all week, feeling like I'm on nyquil during the day. Ive also lost my appetite. My were sore during the "period" but now feel fine. So could I be pregnant? How possible is it?