What is the possibility I am pregnant

[A31814]

On the first week of a new strip of my pill I was 6 hours late taking it(been on it for 2+ years) didn't think anything of it as the pack says if you're less than 24 hours late, effectiveness is not reduced. 1-3 days later I was sexually active without a condom and the next day I had lower abdominal pain after dinner(only lasted for about 2 hours). A few days after that I had an outbreak of whiteheads that cleared up in a day or two. Over the last week or two my nipples have been very sensitive and quite sore but they aren't sore today and now today I have a small amount brown spotting. Is there any possibility I am pregnant? Im 19 and attend university so I'm in the middle of exam season so I have been experiencing extreme amounts of stress in the days leading up to and during the onset of the symptoms. My 'period' isn't due for another 9 or so days and the last one was a lot lighter than usual.