Hi. Actually every alternate day I feel horny and I can't control horny so I do masturbate during the day I feel horny every day it does sex addiction?

That's normal, man. You are nineteen years old. This is happening to every one of your male friends. You build up pressure and if you don't enjoy yourself, you won't be able to focus on studies or get to sleep. I am sorry somebody told you this was a problem. Just ignore people like that. Think about that one special person in your future, and enjoy being young.
When a behavior. interferes w/our ability to function or our comfort level or our health it can be considered an addiction. What you describe does not fall into that category. Peace and good health. If stress is an issue, consider exercise and good food plan.