The best time for a women to concieve is after giving birth. Thats if shes trying. If your not wanting another child right away, which is not recommended this early because of healing time, use protection everytime.
Women are most fertile in the few months after giving birth. If you are having sex at all, there is a chance she will get pregnant again. The best way to prevent it if you are going to have sex is BOTH of you using a form of birth control (like bcp, an IUD, or foam for the woman and condoms for you)
By making sure you "did not incept" did you mean you used a condom/didn't use a condom, did you use the "pull out" method? Women are highly fertile after having a baby, and you should be using a form of birth control to prevent pregnancy. The "pull out" method is not a form of birth control and she can still get pregnant.