Kicking my pelvic ant tail bones?

[happy&healthy]

Quite often, there a thuds where I presume my baby is kicking some part of my skeletal anatomy? Is this common. She hardly kicks my stomach anymore...so that maybe hubby could feel her someday. no she always kicks down below and to the back (which are accompanied by thuds (different from when she does kick my front tummy) Also, since she is always head down at my scans, I think she is thrashing her head in my pelvic region--and I worry she will get a concussion (silly I know).

Does anybody else have this?