i play lacrosse. I can walk fine but when i go to run and sprint, my lower back and under my waist on the left side, it starts to hurt. Its not a sharp pain but my side gets very weak until i relax and start to walk again. Does anyone know whats wrong. I haven't played in 5 days and rested those days. Should i go see a doctor or no and what should i do about it. I started to hurt Wednesday of last week and played until the end of the week. I haven't played since friday. please HELP! Thanks!