I am not sure it's a medical disorder. What about love? Are you a romantic person? Are you looking for something more than sex, e.g., friendship, companionship, emotional closeness? Do you want sex to mean something emotionally to you rather than just a good physical time?

Frankly, you are young and it seems that you have not met the right person and that you lack experience in dating situations. I think you need to set boundaries with yourself - only have sex with people who have meaning to you; people for whom you have feelings and - most importantly - have romantic feelings for you. Hopefully, the rest will fall into place. Good luck to you!