Its possible, its hard to know either way. Doctors don't recommend sex for several weeks for many reasons including that many women are more fertile after childbirth, but aside from pregnancy, you body really isn't ready to have sex so soon after birth. It is the best idea to give it time to rest and heal. I would follow the six week rule from now on and use protection as long as you can after that if you don't want two pregnancies in a row.
There is always a chance to get pg by the pre***. Any time you have unprotected sex there is a chance that you can become pg. I wish you the best and congrats on the new baby! Did you have a boy or girl?