I have had the discharge every month since my son was weaned 10 years ago. I spoke to my Doc and SHE said this was normal. a result of hormone fluctuations. sure enough it is a sign that my period is coming. I dont worry about it at all anymore.
Of course, it can be a sign of more serious issues, but if it is happening every month, and the same time of month (as mine has for 10 years) I wouldnt worry too much about it.