If you don't want to get pregnant then you have to use condoms. Birth control is only like 99% effective when used 100% correctly (which hardly anyone does) and there are so many factors that can mess it up.
So if you don't want babies then you have to also use condoms. It is better that way anyway, cause you are protected against std's, and it helps you not get infections.

But, it could also just be your body. Some people don't get their periods on certain pills. I would wait it out and see what happens, but it wouldn't hurt to call your doc and ask.

I am also on yasmine. Did you mean you didn't start right away on the first day of the 4th week, or not at all that week? Because I usually don't start my period until the like 4th placebo pill. Its been so great, cause I only have like a 2 day period, and even then it is light! So wait it out and see what happens. Like the other poster said, since you haven't been on it long, maybe you havent totally adjusted yet. Keep me posted on what happens!

I started..I guess since it was only the second month on the pill I am not regular..Thanks for ur posts.I ended up startin on the 4th day..Woo..What a freak out ...Thanks