At the first of this year I got a canker sore in my mouth, my doctor put me on Valtrex and this got rid of the sore. But since the first of the month I have gotten canker sores about every three weeks. My docotor said if it happens again he's going to send me to an ENT. My Gastrointestinal specialist tested me for Chrons because of the sores but the test came back negative. What type of things would a ENT test for? Is there anything I can do to prevent getting canker sores in my mouth?