I started the insanity workout program 3 weeks ago (today is day 20). i have started having terrible ankle pains. what is going on and what do i do?

Overuse : You are over training. You must allow your muscles, joints and other connective tissue to properly heal. Stop training until your symptoms are gone. To do anything else is insane.

Take a break: A little less insanity and some ice to the ankles. I think they are being a little overworked. Check and see if you have flatfeet or overly pronate if you do, an orthotic in your sneakers would help take some pressure off the ankles when performing your workouts.