It could be due to a lot of reasons , chiefly since your 26 years old , could be due to an impacted (not completely erupted) 3rd molar. Please do get it checked it soon , also if its a different angle of eruption could be affecting the adjacent molar. White patch needs to be checked too , but dont worry , stress isnt going to help.
Hope you feel better soon.
Next Steps
Examine by a dentist at the earliest.
Health Tips
Avoid biting on the affected side , Warm water rinses.