What Causes Painful Legs Along With Headaches?

My daughter who is 20 drinks lots of lucazade and coke not sue if this is an added problem.she has had pains in her legs for over a year it comes and goes when it is bad she cannot walk properly cold weather hurts them and at one point her toes were numb for several weeks she has been to the Gp several times who has not named anything done Thyroid test Iron usual other blood checks her cholesterol was abnormally low that was all they found now this week the pains are back and really bad headache what could it be what specialist would we pay for as not sure what type Thank you