I think RangoFett was on to something. All hormonal birth control methods can effect a woman's sex drive. Most anti-depressants have the same effect. When I was engaged, I was on the depo shot and was rarely interested in sex. Once I cleansed my system of all the chemicals, I became an insatiable sex-fiend and interested in experimenting in areas that I had never been interested in before.
However, if your frustration and her disinterest are causing conflict in an otherwise happy union, then seeing a provider to have a special need met can actually ease the strain on a marriage. I wouldn't recommend seeing one provider on a regular basis. That can lead to emotional attachment, and I don't think that's what you're looking for. Good luck to you, friend.