Yes it certainly is possible to get pregnant after only have sex once.
But you have to have intercourse around when you ovulate.
Has your cycle returned since you had your baby? If you are exclusively breastfeeding then you are likely to be fine as the hormones associated with that supress ovulation. But if you are bottlefeeding then there is every chance you could become pregnant.
There is not much you can do other than wait and see. If your period is late then do a pregnancy test.
please answer my Q..........