What Causes Vaginal Bleeding After Intercourse?

hi, my boyfriend and I have had sex many times, and I am on tricyclin lo and have been for 6 months and had protected sex once and unprotected sex twice three days ago after doing oral for him and again protected yesterday and I started noticing bleeding last night afterwards and a brown colour today but my period isn't supposed to come until a week from now and I was just curious as to what this could be, because there had been pain all day and I want it to stop