What Causes Vaginal Discharge On Birth Control Pill?

Hello, I am 21years of age, 128lbs and have no serious medical history..I am sexually active and was on birth control for a little..I noticed while on the birth control that i had a lot of vaginal discharge. Today while urinating, I noticed a hunk of white in the toilet..wondering what this could be.. I've never had any complications before and this is quite frightening