I had finished my periods on the 17/01/14 jan and had sex that nite.i now have a light period with light cramps its now 28/01/14?

A one-time symptom?: Many women have occasional variation of their mucus discharge, spotting between periods, a heavier period, a lighter period, or a late or missed period. Causes include: excessive weight loss or weight gain, increased exercising, emotional stress, medicines, having an illness, traveling, birth control pills, hormonal imbalances, etc… if worried about pregnancy, one can do a test 3 weeks after sex.