I was wondering about the depth of the vagina. I've read statistics that say that the average vagina is only 3 to 4 inches deep. This seems way too small to me, since the average penis is considerably longer than that. Wouldn't that mean that most penises would crash into the cervix repeatedly during intercourse? Since this obviously doesn't happen, my question is this: does the vagina actually elongate during intercourse to accommodate the entire length of the average penis?

Dear Alice, 

I take Valtrex daily to protect me from cold sores I get on my face. I haven’t had one since I started taking it a few years ago. My partner gets cold sores on his mouth and has recently performed oral sex on me while having a cold sore. Will the daily Valtrex protect me from developing genital herpes? How will this affect me in the future?

I have recently been advised that my on-going migraines might be caused and/or increased by the use of contraceptives containing estrogen. To that end, I have been recommended to switch to a progesterone-only form of birth control. Which, in turn, basically means I get to choose between Implanon and Mirena (I really can't stand needles, so Depo is out for me!). I am only 23 years old, and have not yet started a family. I do want to have children someday, and am very enticed by the idea of Mirena lasting to the point when I might want to begin trying to get pregnant. However, all of the advertisements for Mirena state that ideal candidates have already had children.

Is Mirena still safe for use in women who have not yet given birth? If so are there any additional side effects to consider in this instance?

I am not sure who the father of my son is. Is it possible to tell the father of the baby simply by knowing blood types and Rh factors of myself and the potential fathers?

What are the risks of HIV infection for the passive partner of oral sex?

My wife and I had our first child last July. Until about 3 months ago, she was unable to reach orgasm at all. Of late, she has very small one's, but they don't seem to be getting much better. Prior to having the baby, she had strong, very quick (3-5 minutes) orgasms 90% of the time. I know the stress of being at work rather than home with the baby could play a part in this. Is this common and is there a way to mitigate the problem? 

If one has a long-term partner and neither AIDS nor any other STD is a concern, is there any medical reason not to perform cunnilingus on a menstruating woman? My significant other is particularly horny during her period and would love cunnilingus at this time. I am willing but curious.

I am curious about double penetration (two penises in one vagina). Because of the increased friction, even if both men are wearing condoms, is there more of a risk that the condoms would break?