Hi there and welcome. Well, absolutely changes in schedule, stress and sleep changes can delay a period. It happens all the time. So, that could be the reason.
however, you also had unprotected sex. (WhY? Please don't do that unless a pregnancy is something you want. We have to be responsible each and every time when we have sex!) That means that there is also the possibility that you could be pregnant. The pregnancy tests may not be picking up the HCG currently, maybe you ovulated a bit later so you tested too early, etc.
Now you mentioned symptoms. Those are also symptoms that a period is coming. Most women do not have a lot of symptoms in very early pregnancy. Nausea, for example, does not start until week 6 or 7 into pregnancy. Reason is, it is the hormones of the pregnancy that cause these symptoms. You don't even have enough hormone to give you a positive result, so you'd not have enough to cause nausea. So, I don't think those symptoms are related to pregnancy but probably more a sign that your period is around the corner.
Time will tell. I think your period is on the way to be honest. No, you don't need to see a doctor at this point. Many women are a bit late for their periods and wonder about pregnancy and if all went to the doctor, no one else would be able to be seen as doctors would be too busy. If you skip a period next cycle due, then call your doctor. Then they may want to see you.
good luck and let us know what happens.