What Causes Heavy Period And Stomach Cramps?

We are trying to get pregnant, last month my period was 5 days early, I took a preg test a week later and it was negative. The past week I have felt very tired, sore throat, stuffy nose, back pain, stomach twinges and cramps (I never usually get anything when I have my period) and today my period has come 4 days early but quiet heavy compared to normal. Could I be pregnant or when do you think I should test again?