all women smell and taste different, some do wash but have glands that produce more scent, sometimes it is diet, hormones, weather, time of the month, equinox any number of things that could upset or rerout the fragile blance we have going on down there. Our anatomy as women is far more complicated and delicate than what you all have hanging. We are also taught from a fairly young age that any variation from "normal" makes us undesirable freaks.
I can't tell you the number of dirty dicks I have run across. Men's underwear; jesus I hardly have known a man who could properly wipe his ass, and that shit is sitting 2 inches away from your jonson all day closed up and hotinside them tighty whiteys. Before you start pointing out flaws in women that actually like and trust you enough to get that close to them, maybe you should be a little more generous in thought. You're not perfect and neither are they, if it's noxious then discreetly hit her up with a baby wipe. (keeping supplies like baby wipes, condoms, lube, in a handy spot is definatly an advanced technique, but very mackish) It may be different and better next time too. If you notice an extreme change for the worse in your regular partner then you might want to diplomatically mention the difference to her because that can indicate a problem.