Can you help me with my canker sores?

I have some sort of hereditary problem in my mouth that causes canker sores. I get the ones with the white/green coating over them. They are very painful, and I get them one to two times a month. They last usually one to three weeks, and get HUGE. I sometimes get to the point where I can't eat, drink, or brush my teeth! Do you have any suggestions to help me get rid of them or the pain? (If you are a doctor, please let me know)