What Causes White Vaginal Discharge?

i started my period today and i just had a really weird white discharge come out. it wasnt creamy or milky looking like a yeast infection. it was really thick, white and hard. about 1 wide and 2 inches long and about 1/2 an inch thick. it was really really thick kind of like hard flesh or something. this has never happened to me before and when i tried researching vaginal discharge i couldnt find any that was described anything like mine