I don't understand... how did your doc even know to check and see if you're pregnant when you hadn't even missed your period? One of two things is possible: either you were pregnant and the embryo just failed to attatch to your uterus, therefore you started your period, or you're just experiencing spotting that occurs sometimes due to implantation. Is it a heavy flow or just light spotting? Good luck, I hope everything works out for you! Let us know!
If you tested positive for pregnancy, then you did concieve, so you are not having a period. You can't know for sure without further testing if the bleeding you're experiencing is "breakthrough bleeding" (I had that in my first pregnancy and everything was fine) or if this is "chemical pregnancy," which is where the baby is lost so early that without a positive test you would have thought it was just your perid.