What Causes Clear Fluid Vaginal Discharge During Menstruation?

I had a rush of clear fluid discharge (vaginally) this morning. It was a large amount. It soaked a pad and went through my clothing. It was like when my water broke when I was pregnant 20 years ago. I am 52 years old, and on day 5 of my period. It was not urine, due to the fact that I went into the bathroom right after, to clean up, and then felt an urge to urinate, which I did. The color was yellow, unlike the fluid earlier. This has never happened before. My periods have been more brutal this past year, with extremely heavy days...wondering if it is hormonally linked?