If I had the opportunity to talk to you in person, I would inquire about what has happened in your life. You were happy before and now are depressed. At some point, apparently there was a change. Did something negative happen? Did something recently change in your life? Answers to these and similar questions might help to uncover the source of your depression.
Your question is whether or not you should try antidepressants. The answer will depend on many variables. It would be advantageous to be evaluated by a mental health professional. The purpose of an evaluation would be to assess your symptoms and to determine if you do in fact have depression. Once you had received objective feedback about your situation, you would be in a better position to choose the most appropriate treatment.
It is currently believed that a combination of psychotherapy and antidepressant medication is the most comprehensive treatment for depression. This combination, however, is not effective for everyone. Some individuals respond better to medication only. Some prefer psychotherapy. If you had tried psychotherapy and found it to be ineffective, I would encourage you to keep trying. Oftentimes it can some time to find the right therapist but finding one could make a major, positive difference in your life. If you decide to try medication, I would recommend working with a child/adolescent psychiatrist who is specially trained to treat depression in adolescents.
You exercise to feel better. Although it does not eliminate your feelings of depression it to some degree improves your mood. For the time being, it is a good coping mechanism. It provides emotional relief and it is a healthy activity. You may also want to try walking with a friend or family member. I understand that you are struggling with social interaction but you should resist the urge to isolate yourself. Social isolation might make your depression symptoms worse.
I would also recommend consulting your parents about the possibility of taking antidepressants. They may have important feedback or advice for you. They may be able to help you with this problem. It might also be helpful if you read more about antidepressants and their side effects. Knowing more information about a potential treatment can help you to make the most informed decision.
Thanks for your question. I wish you well.