Having Light Periods With Brown Bleeding. Experiencing Pregnancy Symptoms. Pregnancy Test Negative. Suggestions?

MY PERIODS HAVE BEEN REGULAR FOR THE LAST 20 YEARS, LAST MONTH IN JAN MY PERIOD WAS ONLY ONE DAY AND VERY LIGHT. THIS MONTH I HAD WHAT SEEMED TO BE A PERIOD BUT WAS MAINLY BROWN SOME DARK RED BUT MOST BROWN LASTED ABOUT 4 DAYS. I HAVE TAKEN PREGNANCY TEST BUT ALL ARE NEGATIVE I HAVE TERRIBLE HEARTBURN , VOMITING , CONSTIPATION , FATIGUE AND SORE BREASTS AT NIGHT PLEASE HELP.