Pain with prone leg lifts

Whenever I try to do movements like frog leg lifts or prone heel taps, my pelvic bone hurts SO BAD. I'm doing these moves on carpet and a yoga mat, and it STILL feels like the whole front of my hips and pelvis are right against the hardwood floor. I don't have this issue when I do swimmers or any variation of back bows. I'm assuming this has to do with my center of gravity shifting to my hips rather than my abdominals (like when I do back bows or swimmers), but I still don't understand why it hurts so stinkin' bad. Does anyone else have this issue? Am I doing something wrong here?