Is my girlfriend pregnant?

My girlfriend and I just started having sex and she is on birth control. Her normal period cycle is the start of the last week of the birth control, which is the pills that don't do anything. We have been having sex and we have been using a condom plus her birth control. It is now 2 weeks past the last week of her birth control and she hasn't had her period. However, she has had late periods before when she is really stressed, and we had a very stressful past month. She takes her pills usually at 10 pm but sometimes takes them at 9 or 11. Could she be pregnant? What should I do? It seems very unlikely she could be pregnant seeing as we use condoms and birth control.