Cumming

Ok I'm 28 years old and I've never experienced cumming before. It's completely frustrating because while I see my boyfriend enjoying oral and sex with me and to watch him cum turns me on. The only problem is out all three of the men I've ever been with none of them has ever made me cum or have an orgasm. And the sex with 2/3 is/was amazing, so it leads me to wonder am I doing something wrong? Ladies help me out how can I cum for my boyfriend?