No barrier method is 100% safe, of course, but Cazzz is right - you're most likely not pregnant and are worrying so much about it that it's stopping your period from arriving. You don't say how old you are, but if you're still young then your body may still be settling into a pattern - you could be as regular as clockwork for months and then your periods go haywire for a while.
As Cazzz says, give yourself another couple of weeks and if you're still worried, speak to your doctor. And try not to worry. ;-)