Is there something wrong with my arm?

Whenever I grip something tightly the middle of my arm aches, as in if the bone is split or cracked. I know it's not carpal tunnel because that's in the fingers. Is this just a muslce cramp or is there something else wrong? Iv told my dad about I but he said it's nothing to worry about (he studied business :P ) I'm 14, could this be because of hormones? The pain gets REALLY bad, and lasts for about 5 minutes. Anything would help :)