I am 14 years old, my friends keep telling me that I could be very sick. I am scared!?

I had almost those exact same symptoms. Go get a blood test because you may have an infection or something worse like hepatitis. Are you really tired? Are you turning yellow (the whites of your eyes)? Does your joints hurt only when you move or all the time? Is the pain in your side on the right or the left side? I would strongly suggest getting a blood test. They can tell a lot better what could be wrong then an MRI.