The loosening and bleeding of gums are a common problem, which can be addressed by scaling of teeth and yellowness of teeth can be addressed in the same procedure. after that proper oral health maintenence would help in getting rid of the problem for a long time. Please ask your dentist if you require modification to your brushing technique and improvements to your oral health regimen

this is not usual at your age - you need to consult a dentist at the earliest as this is be a use of infection in the gums and you would need to undergo scaling and curettage of gums and also would need to be evaluated for flap surgery