Pregnant or not?

Hi! I hope you can help! I was actually supposed to get my period last Wednesday or Thursday (August 4/5), but as of today, Monday August 9, I still haven't gotten it, even though I normally have a regular cycle of 30-31 days. For the past 2 weeks I've had mild symptoms: pain/cramps in my lower abdomen/groin, slight dizziness and nausea. This morning I got what seemed like implantation bleeding once (light pink with mucus), but the tests keep coming back negative.. could I still be pregnant?