It could be that you are pregnant, or you may just be suffering from constipation or an infection. Though you need to take a home pregnancy test(hpt) just to make sure you are not pregnant. Take the hpt 2 weeks after having sex or after a missed period for it to be accurate. Make sure to be eating foods high in fiber(lots of fruits) and also drink plenty of water to get rid of the constipation. If you are not pregnant and the spotting continues, make a doctor's appointment to get checked. Take care.