It's possible that repeatedly missing the pill has made your period late, but 4 weeks is a really long time. Take a test, if it's negative you are most likely not pregnant.
Anytime you miss B/C, especially a couple of them each month, it decreases the effectiveness of your B/C, so there's a chance of pregnancy when you miss them, but not likely. While not taking your B/C regularly can REALLY mess up your cycle, 4 weeks is VERY late for a period to be, take a test, if it's negative I'd say you're probably not pregnant and it's due to the B/C, but just to be sure you can always request a blood test just to know for sure. Good luck!