Have you taken a test yet? You very well could be pregnant.
I was 18 when I became pregnant with my daughter. I know what you are going through and what you will face. Condoms do fail and I learned this lesson the hard way.
Also, consider the effects sex will have on your life. Consider the changes that sex can make in the course of your path. Remember there are other things out there that are more deadly than pregnancy and it only takes one partner to give them to you. Diseases can also last you a lifetime and can affect your fertility, immune system, and so much more.
Also, being a single unwed mother is hard. I have live it! I am now 24 years old and I am pursuing a degree. If you are pregnant, just remember you can still succeed even as a mother. Do not let anyone get you down. It will be a hard road and I hope you will being willing to work hard and will work for success. I really want you to sit down and think about sex. A lot of girls think "that will never happen to me". I thought that and guess what? It did! A lot of my friends also became pregnant. Some have not succeeded and some have. It is all about what you want out of life!