Try good old Harvard bench step:
Stand on a staircase. (or use a sturdy stepstool.)
Step up right, step up left. Step down left, step down right. Repeat until Mark scolds you to stop it with the chronic cardio.
You can walk it, jog it, sprint it, jump it, go up and down two steps, whatever. You'd be surprised how all-out you can go, and you have a railing to grab if you lose your balance.
Also, check your diet -- my understanding is that you should be still losing weight slowly even if you do nothing.
5'0" female, 44 years old. Started Primal October 31, 2011, at a skinny fat 111.5 lbs. Low weight: 99.5 lb on a fast. Gained back to 115(!) on SAD chocolate, potato chips, and stress. Currently keeping food tracker.
I (try to) follow by-the-book primal as advocated by Mark Sisson, except for whey powder and a bit of cream. I advocate a two-month strict adjustment for newbies. But everybody is different and should tweak Primal to their own needs.