missed birth control, light bleeding, possible pregnancy

hi.
I've recently been under a lot of stress, enough that i think it could have affected my period. I've been taking birth control for a little over a year, and my period is normal and occurs at the same time every month. Recently, however, i noticed that i missed about two pills in a row this week, and i started bleeding lightly for about a day or two until i remembered to take my pills again. I also had sex during that week and we didn't use a condom but he pulled out before he came. I was wondering if it was possible to bleed (the blood was also very dark) while you are on birth control not during your period and when you are under a lot of stress. Or even if you are under a lot of stress, do the pills prevent that? I am also concerned about the possibility of being pregnant, even though i am pretty sure i took a pill the night before we had sex. thanks so much for your feedback.