Trying to conceive, possible implantation bleeding? Help

So I had a miscarriage in October 2013 and have trying to conceive again since. Periods have been unusual, but I had a period Christmas eve and was supposed to start on the 21st of this month but instead started spotting (really not even spotting because I only occasionally saw pink or brown when I wiped) exactly a week before my period  was supposed to start. Breast were sore, now they aren't but my period is two days late. I took a pregnancy test in the middle of the day yesterday and it was negative.. Any help/advice?