Could a virus cause you to have small blisters underneath your tongue?
Yes. A flu-like virus can certainly cause this. Stomach upsets can cause this. Ph levels that are off. Also it could be from too much acidity in the body. If one were to eat a pound of beautiful juicy tomatoes they are more than likely to have a very sore mouth and that includes under the tongue. If it continues for 4 - 5 days it's best to have your doctor have a look. Rinse your mouth out 3 - 4 times a day (especially before going to bed) with warm salted water. Gargle (getting it under the tongue) spit out BUT DON'T RINSE YOUR MOUTH OUT! You should also brush your teeth after every meal.