I am 18 and female, what is wrong with me. Possibly Trangular Alpecia

Thinning hair in young women can be caused by many condition, far to numerous to list here. You need to see a doctor who specializes in hair loss in women to find out why you have this problem.  Is this in your family, are you are birth control pills, do you have other medical condition that I need to know about?  These are critical questions that a doctor must know to determine the diagnosis. A physical examination will be critical in assessing your situation as a capable doctor will use a hand microscope to look at each area of your scalp and hair.  This as well as many blood tests are requires to arrive at the correct diagnosis from which treatment can be started and many of them are listed here:  https://baldingblog.com/2009/03/13/woman-with-handfuls-of-hair-that-come-out-every-morning/. The pictures look like a genetic condition called Triangular Alopecia because it is on both sides in roughly the same place. A Hair transplant usually solves this problem.