Rolling Over so soon???

So last night at my parents house we were playing with V (tummy time) and she actually rolled over and started laughing! My Mom and I just looked at each other dumbfounded, and put her back on her belly....and she did it again! We called the guys in thinking maybe we're going out of our mind, and she rolled over a THIRD time! Of course we wanted to keep seeing it but she was getting a bit upset at this point so we stopped torturing the poor child, lol, but I was shocked. And she rolled over this morning too so it wasn't like a fluke-type thing right? I looked in Livis' baby book and she never rolled over until 4 months! V is 5 WEEKS old!?!