Overthinking issue what it could be?

Hello. I really need help. I am 17 yo teenager girI. I am suffering for "overthinking". I can't focus almost on anything so I have some questions. Whether overthinking is related to anxiety? I figured out that I have to get rid of this habit real soon. The only thing I can do now is try to not to think about something little by little. I will try, "Don't think about how to forget something. But I have to think how my life will be if I will forget about ..." overthinking always dont allow me to forget a problem. I will always end up thinking too much about it.... What can I do?