I'd do the hormone workup and then some counseling. Is there any chance that now that he sees you as a mommy he doesn't see you as a sex partner? Anyway, get the physical end of things checked, and then in counseling you could possibly ask him if that mommy thing is the problem.
Many men can start to have hormone issues, even as young as your husband is. I recommend he see the Dr to have his hormones checked. That could be the problem. Is he under any kind of stress, work problems, anything like that? Stress can kill the libido. If neither of these things are the problem then I would recommend couples counseling. It sounds like you have a wonderful marriage and he does love you. I'm really thinking it could be a low hormone problem.