Dear Noonoo,
Well, I am going to read between the lines here.........
In your first sexual encounter at 15, it sounds like you did not have intercourse, but just had oral sex performed on you. You admit that you were anxious and that could be why you did not cum. It would not be unusual to not cum in this situation, especially because it was your first time having some kind of sexual activity.
You did not say whether you had a relationship with the first woman at 15, it sounded like you did not. Your problem might have something to do with the fact that you are not in a relationship with the women you are having sexual activity with. I get the impression that you are having hookups and no real relationships with people you are being intimate with and you cannot cum, which is reminiscent of your first sexual experience.
People are not sex machines and there is a mind/body connection to sexual activity. It also appears from what little you said there may also not be adequate foreplay between you and the women you have sex with to feel close enough to feel comfortable to let yourself go. In addition, If you are having actual sexual intercourse with the women you are with and you do not cum and it is unprotected, this might also have a negative effect on being able to climax as well.
My advice to you would be to develop a relationship with a woman, get close to her without having any sexual activity, with the exception of kissing, and let the relationship unfold for some period of time so that you feel close and have emotional feelings toward her. When you do decide enough time has past so you both feel ready for more intimate sexual activity, go slowly and let that develop as well before you proceed to actual intercourse. Before having intercourse, make sure it is protected sex or that you both have been tested first, have adequate foreplay so that you are both fully aroused and then have intercourse. I would be surprised if this would not clear up your issue.
Good luck with this issue. If this does not change things for you, I would see a mental health professional.