Abdominal issues on one side only.

I've got a couple of question about something I'm worried about. Would be grateful if anyone who knew about this would give me their opinion.

I've been given core exercises to perform as part of a rehabilitation program for back pain and breathing problems. The problem I have is that I can contract the muscles below the belly button as described on the left side but feel no contraction on the right- as if my TA isn't working. Other muscles seem to take over, which makes the problem worse as tight abs is one of contributors to my breathing difficulty.

I'm having a scan next week and am very worried that I have damaged one of the abdominal muscles beyond repair because I can not feel contraction at all. Is it possible that I could have ruptured it or would I definitely know about that?

I was squashed between two cars about 10 years ago in my pelvic region and had horrible pain afterwards. Is it possible that I could have sustained muscle damage from such an event?

I've also felt sensations in that area after overdoing stretching that felt like rubber bands snapping and then heat being given off- does the fact that it wasn't painful rule out any serious damage or does inactivity of a muscle desensitize you to it?