If she was in season and allowed out the house then the answer is almost definatly yes.
Take her to the vet and they would be able to feel for any kittens
If she isnt pregnant get her spayed, if she is once the kittens are fully weaned get her spayed.
If she is fewer than 21 days pregnant, it is very difficult to tell if she's pregnant. You would have to have x-rays done. If you wait a bit longer, the vet will be able to palpate the kittens; however, we should not do that ourselves. The larger nipples are one of the first symptoms, and, if she was out, as Zalensia told you, she probably is pregnant. It's best to have them spayed by six months. Somehow or another, the hormones find a way out of the house and into motherhood.