Sandrea,
It could be possible that you had an early miscarriage, I'm not sure. I wouldn't worry too much about it though. Are you trying to get pregnant? or do you not want to become pregnant? If you have unprotected sex there is a good chance that you could become pregnant. I would not rely on the fact that you haven't gotten pregnant in the past to think that you can't get pregnant in the future. The only 100% was to prevent pregnancy is abstinence.
Kate