Last month I had unprotected(no condom) sex on sept 11(saturday). I am on the pill, however, that Friday was my last day to take it for that month. Then I got my period on either the 13th or 14th. Today is Oct 13(wednesday) and I have not gotten my period yet this month. It usually starts on the Sunday or Monday after my last pill for the month which is on Saturday and it has been that way the whole time. He did ejaculate, but he pulled out so it wasn't inside of me. I took a pregnancy test. It came out negative, but I know sometimes pregnancy test can be wrong. I haven't felt any symptoms of pregnancy at all. I have a lot on my plate though with homework, school, and work and my diet probably isn't as good as it could be so I'm just trying to figure out if those things could cause my period to be late or absent. Help?

Usual stress won't effect most people, but it obviously will depend on the individual as to how much stress is enough to make a change in their cycles.

Since you are on the pill you can consider yourself pretty well protected as long as you have been taking them correctly... same time of day, not missing any, that sort of thing. That the sex was right before a period was due, also decreases the likelihood considerably as well. If you want to decrease the odds even more, be sure a condom is used each time as well.

Most likely your period is just off... which can happen now and then. Give it another week and see what happens, still no period, try another test. If still negative, you could either see your doctor or wait until November and see if you were just skipping your period for October.