Assuming that your only sexual intercourse since your last period was 7 days ago, it is unlikely that you are pregnant. And at 7 days, it is usually too early to detect a pregnancy. There earliest a pregnancy can be detected is about 10 days of conception with a blood test that your doctor can run in his office.
However, nausea after unprotected sex can also be a presentation for a STI and therefore an exam is warranted if you have any vaginal discharge, pain on urination, or lower abdominal tenderness.
Stay hydrated. If the nausea becomes worse, does not resolve, or you start vomiting, then a trip to the doctor or the local emergency room is warranted to evaluate your condition.