What Causes Lots Of Vaginal Discharge?

im 17 years old, 5 foot 3, weight about 9 stone 4lb, my problem is that i have quite a lot of discharge coming from my vagina, i describe it as white and thick also stringy, when i pull down my pants the discharge is stuck to my pants but also the other end still inside of me so its like a string of discharge and i have to pull my pants down further to pull it all out. i am on the contreception pill, could this possibly be the reason for this because i have done a water sample and no infection was fount.