Taking to long to reach orgasm

Ladies, I need your help with an issue. It takes me a long time to reach orgasm. When hubby and I are intimate, I can feel the beginning stages of an impending orgasm, but I normally don't reach it until minutes and minutes after. Which sucks for hubby because once he cums, he tries so hard to remain semi hard long enough for me to cum. We've been married 5 years, and I've reached orgasm maybe 5 times when I'm on the bottom. 80% of my orgasms are reached when I'm on top. Many times I just give up because my arms get tired. It's really starting to bother me and it's all I think about now when we have sex