However, the other day I finally had sex with my girlfriend. It was the first time for both of us.

Well, I was not satisfied with my penis, because it was not fully erect. Is that supposed to happen?

Finally, I need some advice about putting on a condom, because I am having some difficulty with that. So what can I do to keep a firm erection? Would those 'PC' exercises help?

A. Well, I have changed a couple of your personal details to prevent you from being recognised by your friends.

Let's deal first with the famous 'PC' exercises. These are exercises for the pubococcygeus (PC) muscles in the pelvis. I do not think they would be of any help to a guy of your age. They are more for women whose muscles have been damaged by childbirth.

In fact, your story is a common one. Large numbers of young men find that when they first try to have sex, the penis goes a little 'soft'. So they have difficulty in entering the lady. Very often, this erection problem becomes even more apparent when they try to put on a condom.

Now in the great majority of cases, these difficulties are simply due to overexcitement and anxiety. When a male gets excited and also a little anxious about his 'performance', the body releases various chemicals into the bloodstream.

These chemicals include the famous adrenaline. They make the heart race, and the breathing gets faster. Unfortunately, they also make it very difficult to maintain a good erection!

The good news is that once you get used to having sex, matters tend to improve greatly. When you grow more confident, you will produce less adrenaline. And the result will be that you have a better, stiffer erection.

Turning to the question of condoms, many teenagers have great difficulty when they first try to use them. It is quite difficult to put a condom on. So again and again, what happens is the young man gets worried - and loses his erection before he can put on the condom.

Sex experts mostly agree that the remedy here is to ask the female to put the condom on you. Why? Because the average male finds it quite exciting to have a woman roll a condom on to his organ. Also, she can use her fingers to stimulate him, to sustain the erection.

So I really don't think that you have anything to fret about. As the months go by, you will feel a lot more confident in your erection. Make sure you take all precautions not to impregnate your girlfriend.

A. You are right: Worry often delays menses. However, all you can do now is wait for your period. If it does not arrive, take a pregnancy test. It seems to me that you have been treating your body dangerously. Be more careful in the future - have protected sex.

Although these dreams nearly always feature scenes in which I have sex with lots of beautiful girls, there are occasional nights on which they are different. On these few occasions, I dream that some handsome guy is touching my privates and making medischarge. Am I homosexual?

A. No, you're not. Research has shown that huge numbers of people - both male and female - do sometimes dream about fooling around with someone of the same sex. In most cases, this means nothing at all.

It is clear that the great majority of your 'wet dreams' are about girls. That is NOT what gay guys usually dream about! So I am quite sure that you are heterosexual. Quit fretting.

A. There are hundreds of different things that 'could be wrong'. These might be occurring in either you or your partner - or both.

The best way of getting pregnant is to find out your 'ovulation time'.

In women who have regular menses, arriving around 28 days apart, the ovulation time is usually about 14 days before a period is due. The temperature of the body is likely to go up slightly on the big day.

Also, the vaginal secretions change slightly at about ovulation time. They become thin and 'stretchy' - like egg white.

Additionally, there is sometimes a bit of bellyache on the day of ovulation. This is known as mittelschmerz, caused by the egg being released from the ovary.

You can also buy ovulation-detection kits from pharmacies. These are special urine tests which are intended to help you pinpoint your ovulation day.

When you think that you know what day you are ovulating on, that is the date on which you should try to get pregnant, because you will be at your most fertile.

A. No, this is just a foolish old myth.

A. No, you cannot have appendicitis twice. Your appendix has been removed. Therefore it cannot cause you any pain!

Have your belly checked by a doctor.

A. Yes. A single contraceptive Pill cannot harm anyone.