well at 18, osteoarthritis is prolly not the the cause of your pain. i would say ur a bit young still and dont really have to worry about that... yet

secondly ur still growing. maybe not in height... but ur still in a Growth State. (just look at the physique changes from 18-30 year olds) i would suggest:"if ya got pain, don't do it!..." some great words of wisdom to live by. But seriously i suggest taking some time away from the stuff thats bothering that problem area. the body is pretty good about handeling minor injury on its own. A bit of rest a bit and perhaps another active way to kill time is best plan of attack. if several weeks go by and nothing seems to get better, then seek legit medical advice.