I was on the pill for years and used no other method of contraception with it and I'm still not pregnant and never have been. I was very regular but stress was the problem for me, and little thing that I didn't think had bothered me much, and I'd be a week late. I wouldn't worry unless you've been on antibiotics or had sickness / diarrhoea as the other people have mentioned, oh and that you have been taking it within the time slot, you don't say if you're on the combined pill or the mini pill, because you only have a very small time window to take the mini pill in. I say I used to be on it, the only reason I had to stop taking it was I was getting flashing lights and my doctor told me I must come off it, otherwise I'd still be using the pill now. I'd judt get on with it (I know it's not that easy) because worrying that your pregnant will make you even more late!