Why does my left ankle ache when i try to rest? i'm 16 and a jr. firefighter, but worried if this will affect me. i also sprained it a few months ago.

you should have it : Evaluated, particularly since you mentioned you have sprained it a few times before. Continuing to walk on it particularly doing the things a fire fighter does, i.E going up and down stairs while carrying heavy things could cause you more harm. Please find out whats wrong.

Have an evaluation: Most ankle injuries cause pain with activity and not just with rest. When you sprained your ankle you may have injured ligaments , bone, or the cartilage in your joint. It is unusual for minor injuries to cause chronic pain and persistant pain at rest. I would advise you to have an evaluation of your ankle by your local ortho doc. Xrays or an MRI may be needed to make a diagnosis.