What Causes Irregular Periods And Breast Discharge?

I AM 41 YEARS OLD, HAVE A 2 YEAR OLD BABY. I HAD A MISCARRAIGE 5 MONTHS AGO. I HAVE NOT MISSED THE PILL BUT PERIODS HAVE BEEN ERADIC FOR THE PAST TWO MONTHS AND NOW TODAY MY BREASTS ARE SORE AND IF I SQUEEZE THERE IS WHAT LOOKS LIKE MILKY SUBSTANCE COMING OUT. IS THERE ANY OTHER EXPLANATION OTHER THAN ME BEING PREGNANT AGAIN???? I HAVE A HISTORY OF 3 MISCARRIAGES SO AM REALLY STRESSED.