Polycystic Ovarian Syndrome (PCOS) Support Group
Polycythemia is a condition in which there is a net increase in the total circulating erythrocyte (red blood cell) mass of the body. Primary polycythemia occurs when excess erythrocytes are produced as a result of a proliferative abnormality of the bone marrow. Secondary polycythemia is caused by increases of erythropoietin that result in an increased production of...

I have not had a baby but I have had my period start early even while being on birth control. Had the same thing happen, sometimes it would turn into an actual periiod but other times i would just have spotting until my period was due and actually started.
Doesn't hurt to check with your doctor...just don't get freaked out if they think you are pregnant. My doctor insisted that the number 1 cause of spotting is pregnancy and she was wrong. I was not pregnant. Really freaked me and my husband out cause at the time we were not ready to have a baby just yet. I have read in a book about PCOS that spotting can be a symptom of PCOS...
Good luck :)
Its happened to me also. I started spoting a little brown one night, the next day it was red then went kinda brown mixed with red. It didnt freak me out cause its normal for me. Im use to having some browness in my period. Dont worry to much about it but if its really bothering you see ur doctor :)
Good luck.