Robin - if you see your doctor again, you might want to ask him/her what type he/she recommends. I've worn one in the past that's the basic elastic sleeve with a hole for the knee cap. I got it at Wal-Mart (where else??). There are different sorts for more support. I wore mine when I was having trouble with the ligament on the inside side of my knee.
My friend, who is a long-time runner, has worn a type that is supposed to help stabilize the kneecap. It's basically a single thin strap that buckles and velcros around the knee. You put it just under the kneecap, right below the bend in your leg.