Can you have an std if you miss you'r period and are 3 weeks late or is it more than likely a pregnancy?

Most likely pregnant: Pregnancy is one of the most common causes of a missed period. Std's can strike anytime there is unprotected sex and are not necessarily associated with any menstrual irregularities. Sooooo. If you miss your period you can be pregnant and have an std. If this is you we are discussing you should start a prenatal vitamin and do a home pregnancy test and see your doc soon.