Chlamydia is the most common STI and most people wouldn't even know if they had it because most of the time Chlamydia shows no symptoms. Yet left untreated Chlamydia can lead to serious health problems and is the most common cause of infertility. 

If you're between the ages of 16 and 24 you can request a free postal test kit on this website and choose how you would like to be notified of the result, for example by SMS text message.