What Does Delayed Menstrual Cycle Indicate?

Hi me and my husband have been trying for a Baby since July I have regular periods every month. My last period was 16 Jan 15 I'm week late,today, but earlier i got little dark brown blood when I went to loo, then bit later I got some more but looked bit jelly/ stringy. I took a test at 5 days and was negative. Is this my period coming late,or could I be early pregnant?