Girls, my daughter is 22 weeks old but she's already flipping onto her…

Girls, my daughter is 22 weeks old but she's already flipping onto her stomach from her back. She flipped over accidentally once, there was a small bump on the sofa and then she started flipping even on a flat surface, for the first two days she cried, couldn't pull the handle out from under herself, now she tilts slightly on the other side and pulls it out. On her tummy she lies well, holds her head confidently, lays for about 5 minutes looking at toys, tries to reach for them with handles. As she gets tired she starts crying. Our pediatrician says early, around 4 months they should be doing this, in online resources it also writes that from 4-6 months is normal.