What are the chances of getting pregnant on the 4th day of my period?

[Canadamoose]

Hi, so a few days ago, I had an accident. Me and my boyfriend were having intercourse and the condom broke. Now he uses the pulling out method along with a condom, and despite this, there was still a huge mess. When he ejaculated, it wasn't directly on me and I don't know if I got any in me but both of us aren't sure. He thinks there might have been some pre-ejaculation. Now, at the time I was on day 4/5 of my period. The morning after (about 13 hours after) I took a Plan B pill. I also started taking birth control the following Sunday because that's when I was supposed to start (the accident happened on Saturday). It has now been about a week and a half since the incident and since I started birth control. I've been really stressed out, so I'm not sure if it's effecting me, but I've been slightly nauseous, and I've had a bit of brown discharge. I've read that bloating, spotting, and nausea could all be side effects of the pills. What is the likelihood of pregnancy?