Missed period. ,negative results on pregnancy test! What now?? ?

My fiance and I have unprotected sex often. I am now six days late .. Everyday has been more anticipating than the last! I took a home pregnancy test (first response) and it came out negative! On May 29-31 I had some spotting both pinkish and browish. I figured it was implantation only problem is if it was shouldn't I have a detectable amount of HCG by now? I haven't been stressing nor have I had any cramping pains to indicate af. Could I be pregnant?