Stress definitely can affect how long our cycle is as can changes in routine, weight gain or loss, being sick, etc. Your cycle just sounds like it has gotten a little longer in days but is still regular. You don't sound pregnant but just that you're going to have a longer cycle than you used to which is still within normal range. good luck
You are most certainly welcome. We have a woman's health forum you can find under the W's on the community list from the top tool bar or from the communities short listed drop down menu. Come visit us for your gyn. questions. :>)))
Honestly, my guess is you are having a longer than usual cycle and that is all. It does happen especially when we are stressed out. You haven't had sex for five months so pretty much can assume you aren't that far along pregnant, right? So, don't stress about it. Your hormones are just reacting to your stressful school environment. Don't put one more thing to worry about on yourself. Doctors like women to have periods at least every three months. If you go that long, go see your doctor and they will likely give you something to kick start your bleeding. But until then, I sincerely would not worry. good luck on your exams!