CAN I STILL BE PREGNAT IF I HAVE A NEGATIVE BLOOD TEST?

OKAY SO TODAY I WAS RELEIVED THAT MY RESULTS WERE NEGATIVE.BUT THAT STILL DIDNT CHANGE MY FLOW OF MY PERIOD. I STILL HAVENT GOT IT. YES IM 18 AND IVE BEEN UNDER A LOT OF STRESS LATLEY. BUT IM STILL NOT SATISFIED. I CANT EVEN GET A SONOGRAM DONE SINCE ITS A NEGATIVE RESULT. PLEASE I NEED REAL ANSWERS FROM SOME NATURE. TOMORROW IM GETTING A PAP SMEAR DONE. THATS WHAT THE NURSE HAD SAID.SO WHATS THE NEXT STEP.. IM WORRIED =[ PLEASE SOMEBODY HELP..WHATS GOING ON WITH MY BODY>>>??