Safe sex but period late.

The chances of your period being late due to pregnancy are minimal if you've used protection.

Sudden Weight gain or loss, stress and worry etc could cause your periods to be delayed. As you said in your post it could be all the exams causing the lateness. Try not to worry about it too much as this will cause your periods to be delayed even more.

Hope this helps

Just because you use protection,it doesn't mean you can't get pregnant.If you're going to be paranoid like this all the time then don't have sex until you're married. I used to get so mad at girls i dated in the past that would freak out after sex worrying about getting pregnant. It's the risk you take.