Am I Too Sensitive?

I have never orgasmed before. I don't masturbate because I don't like the feeling. However, my boyfriend often gives me oral. I love it but I just can't ever seem to finish. I feel like I get close, my muscles start to tense up and he says I taste sweeter but then all I feel is a numbness and I become way too sensitive for him to keep going. This is so stressful for me and my relationship because I know more than anything me wants me to orgasm and I want to experience it. Is there something wrong with me? Am i too sensitive? Is this normal? How can I orgasm?