I am so confused and scared. Can someone explain?

I had recently made a post with a TMI picture of the blood I experienced on my last period. 48 people said there was no way I could be pregnant with that kind of blood. Nobody said I could be.

I made a new post saying I am on birth control and had that type of bleeding, and now suddenly way more people are saying pregnancy is a possibility still. Now I'm freaking out all over again!

Why can I have that type of bleeding on birth control while pregnant but when you're not on birth control you can't bleed like that while pregnant?

Thanks.