Possible pregnancy

So I was supposed to get my period this Monday (day 27) or Tuesday (day 28). Usually my cycles are 27 days. It's now Friday & I have yet to have my period. I took a pregnancy test yesterday & it was negative. For the past 24 hours I've felt constant cramping like I usually do day 1 of my period but I still have not gotten it yet. Is it possible that I am in fact pregnant? Or do you think my period will come shortly?