like my whole uterus lining came out, preg on birth control?

It can take 1-3 months for your body to adjust to birth control. And if you had a period, you are likely not pregnant. So I wouldn't worry about pregnancy. All the symptoms you describe, I also have around period time and I am on the pill (10+ years).

One of the things the pill does is make the uterine lining inhospitable for a fertilized egg. So that could explain why you saw such a heavy bleed and your "whole uterus lining" at once. Your periods on the pill aren't "periods" they are withdrawal bleeds. Unlike normal menstruation, it is not caused by the natural cycle of hormones that surrounds ovulation, causing the lining of the uterus to be built up (for implantation of a fertilized egg) and eventually shed; rather, it is caused by suddenly taking away an external source of estrogen (your pill), which causes the uterine lining to be sloughed off.

While on the pill, your periods will be shorter and lighter. And please keep in mind, if this is your first month of birth control pills, you need to use a back method such as condoms until you start your 2nd pack.