Possible pregnancy?

Patient: I have been on birth control for 4 months now. My period is always regular. I get it every month, during the last week of my monthly pill package, the different colored pills to be more specific. This month, the week before my last week of pills I started spotting. This continued for 3-4 days of slight spotting. Now I’m on my last week of pills, about to start my next months and have yet to get my regular period. What could this mean?