Hello sir,
What you are experiencing, is presence of hard deposits over the surface of your teeth. It is known as calculus. As it covers your teeth, your regular brushing is unable to properly clean the teeth. This in turn leads to more deposits.
This leads to swelling in the gums, bleeding while brushing your teeth or when your are biting into any food item (like apple), loosening of teeth which causes them to move, and eventual falling out of teeth.
Next Steps
Please visit a dentist for scaling (professional teeth cleaning and polishing service) as there is not much that can be done about it at home. Your dentist will guide you further looking at the severity of the issue. The sooner you go the faster healing can be initiated.
Health Tips
Change your brush in 3-6months.
Word of caution: You are younger to loose your teeth this way. You should seek the help of a dentist before the damage reaches the bone and becomes extensive !!