Usually bumps under tongue are canker sores. These are also called mouth ulcers and most of the white bumps under tongue are exactly this. They appear due to various conditions but usually the prime culprit for their occurrence is virus or bacteria. Sometimes mouth ulcers can even appear due to the deficiency of vitamins and other nutrients in our body.
To get rid of this nasty condition you can try to include yogurt in your diet and apply oral creams directly on the ulcers and medications which you can buy into the pharmacy.
You can also start to take supplements for the deficiency of vitamins or some other nutrients in your body.
I hope that this was helpful in resolving your problem.