Yes, some women ovulate without menstruating and besides ovulation comes before menstruating so this could be ur first ovulation that will preced ur menses and that's why we advice women do family planning after 6 weeks of delivery cos Lactational Amenorrhea as a method of family planning doesn't work for everyone and for some it stops working for them after their baby starts taking additional meal apart from breastmilk. So if u are not ready to get pregnant now, protect ursef. All d best!