How does it feel if three weeks pregnant??

Hey everyone! I need some insight please. How does it feel when you’re first pregnant? Full discloser, I really don’t think I’m pregnant. My questions because:

-I’ve had all the symptoms of my usual periods but I’m 3 days late. I’ve been right on time every month since I was 18 :).

-I have been stressed so that’s why I’m possibility late

-I haven’t felt differently in any way (sex was 3 weeks ago) which is also why I assume I’m not pregnant

I’m actually worried somethings wrong otherwise because my back hurts so bad, cramps even more painful than usual..but no period.

What are everyone’s thoughts? Has anyone else gone through this?

Thank you!