As said above worry and all sorts of other things can cause your period to be late but you need to get some help and advice whether you're pregnant or not, whether it puts your mind at rest and make sure you're fully informed about general sex and contraception issues or you know where you stand and can move on from there.
If you feel uncomfortable talking to your mum about such things, I definitely did, then maybe try and bring up a general discussion with her about sex and such to test the water so to speak.
I've found as you get older that you realise your parents have often been there and can offer you some fab advice and support and it you can talk to her about things then it may help in the future for you to get some help and advice a bit quicker.
If it's still not an option is there someone else you could speak to such as an older sister, teacher, friend or relative.
Try this to find somewhere in your area...
http://www.multimap.com/clients/places.cgi?cli ent=ruthink_01
You can also try Brook for some more info and advice...
http://www.brook.org.uk/
Or RUThinking has some useful links...
http://www.ruthinking.co.uk/
As does Connexions...
http://www.connexions-direct.com/
Whatever happens, don't hide away and panic, there is a lot of help and support out there, you're not alone and it's by no means the end of the world even if it might feel like it.
Hope everything works out for you hon, let us know how you get on xxx