Unprotected sex is very risky behavior and adding multiple partners to this situation increases the dangers greatly. Unprotected sex puts you at risk for contracting numerous STDs, HIV and unplanned pregnancies. You may not know all of your partners' sexual history, which can put you at risk without knowing it. You should be greatly concerned about these risks.
Although you have not gotten pregnant yet, there is no guarantee that you will not. It may only be chance or luck that you have not gotten pregnant so far. These sexual encounters are in no way a predictor of your fertility or future chances of getting pregnant. Yet, understand that unprotected sex, with any partner can result in an unplanned pregnancy. If you do not plan on getting pregnant, please use a method of birth control.
Since you are sexually active you should always practice safer sex. This includes wearing a condom! You need to know your partners history in order to safeguard your own health. You may also want to see your doctor or visit a local Planned Parenthood or local teen center in order to discuss birth control methods and any other questions you have. If you live in northern NJ, you can call the Adolescent/Young Adult Center for Health at (973) 971-6475.