What Causes Vaginal Discharge, Abdomen Pain, Missed Periods With A Uterus Sac?

I've been having a lot of thick, milky white vaginal discharge for the past two months and pain in my lower left abdomen. Didn't have my period for 2 months...My gyno said that I had no infections and did an ultrasound. She found a water sac in my uterus and said it was nothing to worry about and to come back in two weeks. What could be going on?? HPT tests came back negative...And the only thing a doctor found was that I'm Anemic.