Can’t orgasm?

I’ve been dating my boyfriend for 3 years. Out of all the times we’ve had sex I have only orgasmed maybe 3-4 times.. I don’t know what’s wrong. I don’t know if I just think about it too much or what. Please help me, it makes me feel bad knowing that he thinks it’s his fault and that he just doesn’t turn me on. I don’t want him to think like that.