What Causes Vaginal Tissue Discharge With Light Menstrual Bleeding?

Hi, I ve had irregular periods for as long as i can remember. The last time it came was around mid December. I had sex On Jan8 and took postinor about 14 hours later on the monday ,just in case. Again had sex on the wWednesday didn t ejaculatwe in me but took off condom coming down to the end and took postinor about 1-2 hrs later .had sex again on the Friday ,twice and without condom for about 1 minute but there wasn t any ejaculate. I have had odorless brownish discharge on the Saturday and Monday16 during the day.In the afternoon/evening it turned into bleeding and i experienced period pain. Later that night I saw that, what looked llike the lining ,came out . I never saw it that size before, was not huge but not tiny..had consistency of chickenskin but not as thick. The bleeding slowed down and looked like brownish blood but not heavy at all which is weird as the second day of my period would be heavier than the first. It looked like if it was the ending of my period. I googled one day period and the first thing Isaw was tthat I could definitely be pregnant. Is this true? Is this the side effect of the postinor? (The bleeding) should Iworry???? Please help. thanks you! Freaking out over here