I Am A 14 Year Old Boy Who Is 6'

I am a 14 year old boy who is 6' 1" and whenever I work out for the past 3 weeks, I get a really bad headache. I am forced to stop because it hurts so bad. And last week whenever I run, my legs hurt really bad. I am so frustrated because I want to work out but the pain is too much. I had an MRI and an MRA last week and the results came back normal. What do I do now?