Why Is There An Indentation In My Thigh?

Im only 18 and i had a slight indentation in my thigh and began noticing it a couple of weeks ago. im only 5'2'' and wiegh 124 , i havent lost or gain wieght? i do sometimes have pain in my knees but rarely and im use to it. but now this indentation in my thigh has increased?? its very noticiable even my parents think its wierd. im very confused and i dont want to push everything aside to make an appt if its nothing serious?