Since you are a young person chances of having osteoarthritis is rare. Generally athletes get ligament tear, in common words sprain due to excessive rotational force which will cause pain if not healed properly. Since you can able to walk and withstand the weight of your body normally from past 1 month chances of having fracture is less, so its a high ankle sprain which would have happened while you are playing football, generally it takes 6-8wks to heal but if you resume your athletic activities in between without taking rest, you will have pain again. So consult a orhopedician for further management.