Hello, I am a gum specialist. Looking at the picture I can clearly make out that u have a shallow vestibular depth and u do not have much attached gum, which withstands the chewing forces. Because of that, the gum has receeded down along one tooth, because of which plaque accumulates and it always appears reddish and is painful.
What needs to be done is - u need to visit a periodontist (gum specialist) and get teeth cleaning and polishing done. After that you will have to get gum grafting done to correct this problem. It’s a chronic recurring problem that will worsen with time and you will lose your tooth, if not treated.
Next Steps
Visit a gum specialist (periodontist) because he/she is the correct skilled specialist to solve your problem. A general dentist is not geared with the skill to treat this problem.
Health Tips
U can search for periodontist on practo in your city