spotting 2 days after period stops?

Ever since the birth of my son I've had very predictable periods...29 days, 4 days long, nice and consistent...this month I started on Monday the 25th and it lasted your typical 4 days...today however I had some brownish spotting (no smell itch or burn present) and we are trying to conceive so I've been taking hpt like crazy and obviously thought I was out when I got my period...has anyone else had something similar happen? I'd love to have your thoughts, thanks!!