could I be pregnant???

Ashley
Hi so 3 weeks ago, I had unprotected sex. He did NOT ejaculate. I took plan b 2 hours after. My period then came a week early. Immediately after I had my period I then have started having cramps in my lower abdomen and vagina. Today and yesterday I have been feeling nauseous with the sensation to vomit. The day after my period ended I took a pregnancy test and it came out negative. 
I am extremely scared bc Im afraid my "period" could be implantation bleeding. I do know that implantation bleeding is on and off while period is a full 4-7 days. BUT implantation bleeding occurs usually a week before period and then you miss your period, and it is coupled with pink or brown discharge. I had my period for 5 days, and then 2 days of pinkish "discharge". It was more like fluid but it wasn't necessarily the consistency of discharge. 
I am freaking out bc I don't have health insurance and I'm in college.