Can someone here tell me please how to get rid of an mouth ulcer that hurts?

Laser: If you see your dentist he or she can use diode laser to zap the ulcer which stops the pain, cuts the cycle in half. It works great!

Keep the area clean: I assume the mouth ulcer is so-called canker sore whick will heal in 7-10 days if it is not infected secondarily. Keeping the area clean via thorough oral hygeine is by far the most useful remedy. Avoid spicy food, rinse after each meal, and apply topical anesthetics if pain is severe. Good rest is also helpful because stress and immunity play big roles in this disease.