What Causes An Increase In The Discharge During Menstruation?

hi doctor.i m 21yrs old. i started bleedin after 19days my last period ended. i was sexually active during my ovulation time. i took a contraceptiv pill almost near 72hrs later. 3-4 days frm den,my discharge has been increasin.. got white,light yellowish also.. den found dat m bleeding too.. so got a velocit test.. it showed negetive.. i hav heard of implantation bleedin..but test is negetive.. wat shud i conclude? m i not r m i pregnent?shud i consult doc?