Hello Welcome to HCM. Masturbation is not a problem. It is not any type of addiction like tobacco or alcohol. It is a good thing. The penis which is doing in vagina, in masturbation it is done with hand, so you are getting same pleasure. It s normal in your age dear. But don t involve your whole mind in it. You should concentrate in your studies. For that, take deep breathes and take do some exercises. Take help from elders in your families. If still problems with concentrations, consult psychiatrist or psychotherapist for help. Don t worry and take care... All the best for your studies and good results.