Red lines spreading on my left and right thigh?

Hi,
Im 15 and about 108 pounds and about 5'2
I have notices a few months ago about two lines on both my thighs. They started out small and when i rub my finger i can feel them indented a small bit. Over next moths they began to grow and more started to grow (these are located on my inner thighs). Now they are deep red and very noticable. People and friends in my highschool ask me if i got scratched on my legs because they resemble scratch marks. I complain to my mom about how i hate them but she thinks its all do to growth or chafing. We can only think it has to do with growing, shaving, or maybe my shorts rubbing my legs, but the marks started lower than my shorts. I really want to know what these are because im really embarassed to wear shorts or bathing suits and i want to know if i can use or take anything to have these go away. PLEASE HELP!!!