Thank you for the question and thank you for visiting our site. If you are having unprotected intercourse and are late for your period, then pregnancy is a distinct possibility. You must check a pregnancy test now. Symptoms of pregnancy include nausea, fatigue and a delayed period. The pressure feeling in your upper stomach, if related to pregnancy, could be related to reflux related symptoms (reflux of stomach acid). Again, all of these signs point to pregnancy and you should check a test as soon as possible. We are happy to help you sort this out further once we know the results of the test. I hope that this helps and good luck! Dr. Tim