I have been happily on the pill for two and a half years and you could set a clock by my periods…never late and never a variation by moe than an hour in the time and day my period starts. My bf and I also use condoms. Last month I did not miss a pill, nor were there any unusual condom incidents (breakage, leakage, slippage) or anything that would lead me to believe there was anything that could remotely cause me to suspect I could be pregnant. Yet when the day and hour came last week…no period. As a matter of fact, the entire week passed without starting my period. Yesterday I started a new pill pack but i never had last months period. I’m a little nervous. I don’t feel pregnany and I can’t logically see how I could be. But I am thinking something isn’t right. Maybe this merits a call to the doctor. Does anyone know of any other reason this could be happening? I am 36 and a little young for menopause. My mother didn’t begin menopause until well into her 50s, so I don’t think that is it. Could it be stress related? 
I’d take a pregnancy test just to be sure…
Could be stress, could be lots of things! Give your real doctor a call and see if they want to see you.
Good Luck 
It can be stress related or excersise related-it could be many things. The first thing you need to do is take a pregnancy test (that is the first thing they will do a dr’s office) and make a dr’s appt. ( This could indicate something mild or something severe-either way don’t wait it out or ignore it.)