I will try to be as specific as possible. I am 19 years old, I started having periods at the age of 9. At first my cycle was 42 days but for the past couple of years it has been exactly 35 on the dot.
It is now the 10th of March 2010, and I haven't had a period since the 28th of December 2009. I had unprotected sex on the 16th and 17th of January 2010, which I believe is when I was fertile.
However, I have not had many of the common pregnancy symptoms and have done 4 home tests that all came out negative.
My question is, in spite of this, is it still possible for me to pregnant, or is it more likely that something else is causing me to miss my period?

The matter is very worrying for me so as many answers/opinions as possible would be greatly appreciated.

Thanks

It could be either.
It could be that you are in fact pregnant.
Or it could be just that your period is delayed because you are stressing about it.

There are a lot of things that can throw your period off from diet, to stress, to medications.

If you are really worried about it make an appointment at your doctors to get a blood test done :)