can any body give me some advice???

me and my bf have been trying to get pregnant and about 3 weeks ago i got cramps in my lower stomach which was around the time i would have been ovulating, i went to the docs who just booked me in for an ultra sound. this isnt till next friday tho! i have had tender boobs, feeling sick and feel tired. i came on my period and it was heavy to start with very red blood then completely slowed down and the blood turned alot darker like brown. it only lasted 2 days! i did a pregnancy test which came back negative? could i be pregnant or just living in dream land! please help! %-)