CANNOT ORGASM

So I've been with the same guy for over three years, and I have never EVER had an orgasm. The sex feels great but I just never can climax no matter what I do! He spends plenty of time down there I just cannot ever reach that point. I also don't know where tf my g spot is. Please help! Also, I have tried to do it to myself (weird, I know) just to see if I can orgasm and I cannot. This isn't normal?!