There was almost a word for word post in another forum, I don't have time to look for it now, maybe tonight.
Anyway, get her hormones tested by an endocrinologist. Gynecologists aren't the best for this shit unless they have a subspecialty in endocrinology.
But I gotta tell you, when you meet a 23 or so year old woman, you love her and she loves you but she could take or leave sex, or she was never particularly interested in it, that is NOT an indicator that she's gonna turn into a nympho down the road, m'kay?
Horny women who completely lose interest = problem.
Women who were never particularly horny to begin with being even less interested now they're in a committed relationship = normal.
Having sex less than you did when you first started going out after being together three years = very normal.
See what I'm getting at here?