If you live in the UK, go to the doctors (it's free after all!) and check what they say. There could be factors which are affecting your period - a cold/flu, weight change, that kinda thing, however given that it has been 5 days now I would go and get it checked, perhaps leave it another 4 or 5 days (if you can stand the wait!). Oh, sorry, noticed you mentioned dollars, not pounds.... are there any free pregnancy clinics where you live? If it's free, use it! At least you would know, and also if there are any other reasons that you are not having your period, then these could be identified... it's not something you want to leave un checked!
Good luck!