my son is 17 years old. He plays football. He has developed a high hamstring problem and it has not healed completely in two years. He originally injured it doing squats in the weight room. It healed and was injured again several times in the past year running drills. It seemed to have been healed and he did it again this week back in the weight room. it is a pain up near his glutes.

what can we do to a) heal it
b) stop it from happening again