You might check to see if you have an intolerance to gluten. This is contained in wheat, rye, barley and oats. I am not sure if gluten intolerance and celiac disease are one and the same, but people with celiac disease can't tolerate gluten, and one of the very common symptoms of the intolerance is canker sores.
No one is sure what causes canker sores. A slight injury while brushing the teeth or eating abrasive food tends to produce canker sores. Emotional stress is a factor. Take 3 or 4 Acidophilus capsules 3 x a day for the first day and 3 or 4
two times a day the second day and 3 or 4 once a day for the 3rd day and thereafert until the canker sores are gone take 3 a day.
you can get these at a health food store or in the grocery store in the vitamin section.
reflux is quite common but the sores sounds to me like your alergic to something ...milk perhaps.