What Causes Vaginal Bleeding Post Unprotected Sex?

My boyfriend and I had unprotected sex and he came inside of me almost 4 weeks ago. 6 days after we had sex I started spotting a brown discharge and this lasted for 12 days, on the 12th day it turned into a normal flow period and on day 19 of blood it finally stopped. Day 20 (this morning), we had unprotected sex and he came inside of me once again. directly after, I started bleeding bright red blood and have been spotting all day. Now There is only blood when I wipe but it is brown/red and very clotted and gummy-like (hard to explain). What can this be? I went to the doctor on day 13 of period and all they told me was they think I have PCOS and that my periods will probably always be irregular. What is wrong with me? Keep in mind that I have had irregular periods since I started having periods, before this period, my precious period was in December 2014.