I can't orgasm!

I'm 18 years old, and have been with my boyfriend for 3 years now. We both lost our virginitys to each other. The problem is, I have never had an orgasm. As sex goes, we have both learnt from each other and it is pretty amazing, but when it comes to me having an orgasm it takes lots of work and when I feel like it's about to happen, it never does it just goes away. The feeling builds and builds, then stops and I go numb. It is so stressful and I have experienced this my entire sex life. It is so frustrating it sometimes has me in tears of anger. My boyfriend is so understanding and he hates it for me. Please I need some advice, is something wrong with me? I have the contraceptive of the implant, and I have had this our entire sex life too. Help😫😫😫