Spotting & birth control-- could I be pregnant?

I started taking Lo Loestrin five or six months ago, I can't remember exactly, and I've been loving it-- no side effects & I actually lost weight. Skip to yesterday, it's a little more than halfway through my cycle and pill pack (cycle day 19). My boyfriend and I have been having sex regularly and I've been just about perfect taking my pills, the only slip up this month was that I forgot to take it with me to a friend's house earlier this past weekend, so I was about 2.5 hours late taking it, but I took it the minute I got home. Then yesterday, I woke up to some brown spotting in my underwear. Nothing too crazy, but enough to put on a liner. I was having some mild cramps, and I had a little more brown discharge throughout the day, but not even enough to need to change the liner. By the end of the day yesterday, it had stopped, so I went to bed and woke up with nothing, just normal discharge. So I went on about my day and just a few minutes ago I started feeling some more cramping, went to the bathroom, and there it was again. It's pretty dark brown, but a very light amount. I know that spotting can be a side effect of the pill, but this hasn't happened to me since the first month I took it. Any thoughts?