I had my period March 5 thru the 10th. On Wed March 11th I had sex,and it was unprotected. On Tuesday March 17th I began having some light bleeding like spotting. It stopped and then started again at around 9 am on Wednsday March 18th and has continued thru today. It has been a light pinkish or brownish color. I have always had a normal period and have never had bleeding or spotting between periods before or after sex before. I was planning on calling my OBGYN on Monday,but what could be the cause of this?