How to deal with the pains of a teenager ?

hello everyone i`m a 15 year old boy with alot of pain on the inside. I`m haveing trouble figureing life out,recently i`ve changed school and was forced into makeing new friends. Most of these people don't understand me. Also i recently have lost a girlfriend of 5 months and im heartbroken. and recently one of my closest family friends died, of undisclosed problems. i know most of these problems happen in life but yesterday i visited a docter becuase of knee pain and i found out i may never be able to play sports agian. i`m very worried about the rest of high school and life im not sure were my life will go or if ill be anything in 10 years im worried 10 years from now ill be jobless or single without kids. im so worried about the future and what it holds. if anyones out there please comment and try to help im not sure how to think or feel about now or the future. i dont know how to feel and i sure dont know were to go.