I had sex 8 days and 1 day before I got my period. It was very light only lasting 3 days with no heavy flow. Now I have nausea , breast tenderness and frequency. Could I possibly be pregnant?

Yes that happened to my friend! And than she found out she was pregnant

Yes, you did not mention any birth control, but even with it, it is not 100 percent.

So yes there is a chance,

Only one way to know for sure, take a pregnancy test.