Doctors wouldn't know much about this, more like a coach or a gym trainer's question. This is a good place for this also, I guess we can fit it here!
So basically, want you want to do is work that weaker side. Even though this video may sound stupid, it gives different ways of working both sides of your abs evenly: http://www.youtube.com/watch?v=sWjTnBmCHTY
Those are just some examples. You can do oblique crunches, or just regular crunches on one side. Curls...I don't see the difference between those and crunches, but I and a lot of others say that crunches are better for ab workouts than sit-ups (just for future reference).
So yeah, there's more than one way to work the abs. It's not that big of a deal and you can fix it if you get on it immediately
You probably want to go to your gym trainer or coach anyway for some more ideas and info on what you're doing wrong.