Whatever communication style you've developed with your child will carry with it rewards and drawbacks, and likely will be the template for conversation for the rest of your lives. Ideally, your kid will believe he or she can ask you anything and get some semblance of a straight and honest answer.
Whenever your kid brings up a topic you'd rather talk about later, it's easy to deflect the touchy subject by saying, "We'll talk about that when you're older." Do it too often, though, and you'll quite likely not be asked again. In fact, you might not be welcomed to share your thoughts on that matter at all.
Always attempt to answer your kids' questions to the best of your ability (making concessions for age and maturity), so that they'll keep asking those questions as they grow older. And as your kids grow into teens, pay attention to whether they're still asking questions.
If the unexplained relief you've been feeling lately is because you're no longer being asked far-out and discomfort-inducing questions, that's not a good thing. Keep your thoughts accessible to your kids, and if you don't know the answer, help them find it.
The next aspect of talking to your teen about sex without embarrassing them is totally going to embarrass them.