I've Been Having Unprotected Sex And I'm Not On Birth

I've been having unprotected sex and I'm not on birth control. Last night I felt shooting pains hitting my cervix accompanied with cramps, almost like contractions. It lasted about 10 minutes and then abruptly stopped. Now today, I've had cramps continuously with no end in sight. Also, a fullness feeling in my lower abdomen. Took two pregnancy tests today and they both came out negative. Not to mention I ended my period earlier last week. Is this a sign of early pregnancy?