Some ideas...
I'm hoping that I can give you some sound advice, only because I have a sister who works out with me on a daily basis and she has a lot of foot problems.
My sis usually tries to concentrate on the moves, usually opting for a more or less low-impact version of Cathe's moves. When she goes into a high-impact segment, say plyo jumps, etc., Molly jumps gingerly and not very high but she still manages to get her heart rate up.
The other thing that I would suggest is a bone density test. Maybe, just maybe, and I'm not a doctor...you have the onset of osteoporosis or some bone thinning. It's just a thought and I'm not trying to scare you. Many active, young women who also do weight training have this "silent disease." It's worth a shot. Some risk factors include family history, never having babies, small frame, if you are pre-maturely gray and a myriad of other factors, I would definately check it out.
Good luck and I hope I was of some help!