My gf missed 5 days of her birth control this month she has taken two prenancy tests both negative but now 6 days late on period any ideas?

Pregnancy. She should have a laboratory pregnancy test done. If she is having difficulty with birth control pill compliance, perhaps she should see her primary care provider or a gynecologist to explore other birth control options such as Implanon, the IUD or the depoprovera shot,
Do another test. Repeat another pregnancy test. Stress, excess physical activity may lead to menstrual cycle delay, but pregnancy would be the most common, and obvious cause.