My 17 Year Old Daughter Has Multiple Bruises On The

My 17 year old daughter has multiple bruises on the outside of her legs from her knee up to her thigh/hip area. At first we thought they were due to soccer games/contact but, it's been months since she played and more bruises show up. The general practioner took some blood and tested urine but so far nothing has shown up as abnormal. I'm wondering what the next step should be - what type of doctor should we see next.