What does an early period that lasts two weeks mean when you're on birth control?

It's called breakthrough bleeding, and it's not uncommon with the pill. It can be caused by stress, and if you had that heavy a period twice in a row, you certainly shouldn't be pregnant. If it happens again with this next cycle, you need to call your doctor and probably get your pills changed. You need to take a multivitamin with iron to build yourself back up after losing so much blood.