I need a bit of advice

Well we had unprotected sex on Monday the 31st, I was just ending my period and in the spur of the moment he came inside. Now I do take birth control, I started it the next day because my days are all messed up with when the prescription is filled. Today, I am spotting and have like a week and half left of my pills. (22 day) low estrogen. Is there a slight chance I could have ended up pregnant? I mean I take it religiously, and for 6 years. But the minor slip up I'm worried about... but I mean wouldn't a week be too early even if? I don't know.  I doubt it but it's just a little weird  Since I am cramping and it's very light colored