Definitely check with your doctor before you do any more exercise of any kind, okay?
But once you have, as long as your doc. says it's okay, you might try Pilates (lots of videos are out there...I love Denise Austin's 20 min. Yoga/Pilates mix)...it's a gentle way to increase your ab strength. You may also try other variations of crunches...like a reverse crunch (raise your legs up and lower them), lowering your torso down from a seated position (rather than raising it up from a lowered position) etc. Your doctor may have some, or you can find some online (check with the gurus in our Exercise forum, too) and have him or her review them.
Good for you for exercising, but check with your doctor, okay?