hi i am 15 years old yesterday i was playing football on a grass field outside my house.i was playing in goal when my friend took a shot i ran accross the goal to stop the ball at this time i was wearing no shoes and the grass was wet my lead leg (left leg) slipped and i fell down quickly awkwardly putting pressure on my left leg in turn putting pressure on my back i did not notice any immediate pain although now the next day it is sore in the upper middle of my back and awkward when i move. should i be worried or should i just relax (it is not causing great enough to disable me from walking cycling etc but is still sore.