my last period lasted from october 25th to the 30th....i was expecting it to be back about the same time this month, november 25th but it is now 4 days later and i've only just began to spot very lightly about 20 minutes ago. my boyfriend and i have had protected sex in the last four days, but prior to that we haven't had sex in almost three weeks. our sex is always protected and i don't recall any slip ups that may have had me concerned that i may become pregnant. i really don't think i am pregnant because i feel none of the usual symptoms, but this is strange because my cycle is usually very regular. could it be implantation bleeding? are there other symptoms i should be feeling if i am pregnant?