That's not uncommon, especially on longer rides. The best solution I've found is to buy a female specific bike saddle. They're shaped a bit differently and are much more comfortable if you're going to be riding a lot. You could also look for padded bike shorts, again there are female specific designs made to soften the ride a bit...I've never used them but a friend of mine really likes them, and I think they're probably less expensive than a new saddle, so it's worth a try.