i'm 15, and have a strange muscle problem, complete mystery, have been for 3 years, I NEED HELP :(

i have had a muscle problem for 3 years, it started off as just shaking, physically of my arms and hands.  it now makes me get bad headaches that last the whole day, making me feel like someone is pushing my head together to pressurise it.  and i get aches in my legs and arms and sometimes a weird stomach muscle pain.  i also get random muscle firings every now and then.  i'm off sport because i can't cope with it because any exercise makes the pain in my legs worse.  i need help, i've had 4 scans, thousands of blood tests and so many doctors and i'm still a mystery.  i'm 15 and its ruining my life, i used to love sport.  help, please.