Looks like you must have got mouth ulcers. There can be a variety of reasons for mouth ulcers. One of the reason can be a small viral infection called as herpes labialis. It heals on its own in 7-15 days and has a characteristic sign of cracking near the lips on affected side.
Next Steps
You can take some pain killer to relieve yourself from discomfort because of ulcers
Health Tips
Don't share your utensils like glass and spoon with others till it heals completely,as you may transmit it to other family members. Take more fluids in your diet