C section questions?

I give birth in a few months and i’m so scared because I hope I have a vaginal regular birth. But at the same time, I can’t even fit a tampon in me or it hurts like hell so i’m super scared that I won’t be able to even get the baby out safely. Do they tell you ahead of time you need a C section before you go? How do they know if you need one weeks before? This is my first birth and I really want to know! Thanks