If you aren't rubbing your genitals together at least occasionally, then you're just friends.

It's kinda obvious that the girl has a normal sex drive. She is probably fucking someone else. They are both way young and live far apart. No need for her to go through a battery of medical tests just to find out that she is in into her boyfriend anymore.

Or she might have other problems. People who were victims of sexual abuse as children sometimes have a hard time coming to terms with sex as a consenting adult. If this is the case, therapy is what she needs, and an understanding partner who is willing to work with her to help her overcome her issues.