If you experienced a missed period this month and last month there is a chance that you may be pregnant. When you are not pregnant the lining of your womb is refreshed each month (just like your mobile account) and the old lining comes out of your body in the form of your period. However, if you are pregnant this doesn't happen, that same lining becomes the incubator for the group of cells that may one day become a foetus, and that's why you dont get your period.
If you are sexually active, and feel there may be a chance that the missed period is related to unprotected sex it's time to get a home pregnancy test. They are a quick, inexpensive way to get back your sanity. So if you are scared to do this with your mum, get your bestie to come with you to the chemist or pharmacy. The tests are pretty easy to use and really help set your mind at ease. If the test comes back positive, you should make an appointment to see your doc and it might be an idea to speak to the parentals.