What Causes Vaginal Spotting After Unprotected Sex?

Hi, me and my boyfriend had unprotected sex last week and he Did ejaculate in me.This week I started spotting then started bleeding for three days.I had nothing for two days after and today just noticed a pink tissue like discharge when I wiped and floating in my urine. Oh and I have been taking the depo shot for five months and never had a period since I started taking the shots. Curious what s happening?