What Causes Diluted Flow During Period Along With Muscle Twitching In Vagina?

Hello, I am a 39 year old, experiencing something very different during this months menses. I started this morning and I have felt vibration/muscle twitching all up and down my vaginal wall and into my uterus. Not painful. Only my usual cramping and my flow seems more dilute with clear fluids than usual. I am healthy, great BP,CHOL ect. I am overweight and started exercising 6 days a week and on my 3rd month having lost 12 lbs thus far. What could be causing this?