Agonisingly excruciatingly painful.
And as an endometriosis sufferer, I was no stranger to pain.
First one. No build up. Contractions started every 2 mins, then 1, and lasted for 16 hours. No. Break. At. All. Hour and a half to push. Waters broke at last second. Pain of contractions was worst period pain x 1000.
Second. Waters broke first. Intense again, no build up. Minute apart, lasting a minute, no let up for 8 hours. But 20 minutes to push.
Third. Intense again, but more of the standard build up. Got stuck in transition. This was utter hell. For hour and a half, then pushed out.
And the after pains, fuck me. After number 3, they are like the worst contractions all over again.
Anyways. Probably worst sensation is the crowning. It burns like hell, but those magical words of 'just pant now, babies head is here' is pure heaven, as once head is out, you're pretty much there.
I loved gas and air, couldn't have done it without it!
Good luck OP x