[20 Dollar Nose Bleed]

It's very VERY unlikley that you'd be getting symptoms of pregnancy so soon.
It takes about a week for a fertilized egg to travel to the right place and plant itself in there, until that happens then nobody is properly pregnant and even after that happens it can take several weeks and sometimes months for symptoms to start an seeing as you said you only had unprotected sex about a week ago...nah. If you are pregnant then the egg would only just be implanting itself right now and the chances of you having symptoms are almost nonexistant.

You may just be experiencing signs that your period is due.
Are you scared of being pregant? If so then maybe this could be your wake up call to start using protection. If you're happy about the idea then cool beans. =]