TeenHealthFX is glad that you wrote. You certainly don't have to feel strange because of your age. We have many people write into the site that are not technically "adolescents", but are concerned about their health like you are.
If you had unprotected sex, or sometimes even if you did use some birth control, there is always a risk of pregnancy. It is possible to have a very light, irregular period in the first few weeks of pregnancy and home tests can be inaccurate. What you really need to do is go to see a doctor, get examined and take a medical pregnancy test so you will know what is going on for sure.
Being sexually active also requires that you be responsible for educating yourself on how to prevent pregnancy and avoid sexually transmitted diseases, and the precautions you need to take. So regardless of whether you are pregnant or not, TeenHealthFX recommends that you see a medical professional to discuss safer sex and birth control methods.
If you do not feel comfortable seeing your own doctor for this, FX recommends going to your local Planned Parenthood for an appointment.