You are on the cusp of forming your identity, a daunting task for all of us, and my guess is that as you are ending your high school experience and moving toward the unknown there is a concern about your future. Very natural; very understandable.
There are three things that I would suggest. First, I think you need to have a plan about what you want to do over the next year. What kind of experiences and education do you want to have? If you are planning on being a musician you will need a plan about how to grow into your profession. Who will you learn from, what instruments do you want to play? Who do you want to play with?
Second, you need to broaden your circle of friends. The more connections you have at this time in life (indeed, at all times in your life) the happier and better off you are likely to be. Make new friends and do new things with them.
Third, don’t wait for things to get worse. If you do not feel better within a month I would make and appointment with a therapist to assess what your situation is, and what possible options are available to help you feel better. The find help tab at the top of the page will connect you to someone in your country.