I have had 3 labour's, 1&3 back to back.
1st one was awful, was sent home 3 times as apparently i wasn't in labour, wasn't dilated, nothing going on front end, go home this is the part of labour no one warns you about, take some paracetamol. Went into labour around midnight, was finally admitted around 9am and delivered at 11am. Luckily the shifts changed at 8am and the new midwife was horrified i had trailed backwards and forwards and had no pain relief, was too late for anything other than pethadine and gas an air. Labour was mostly done in the house in agony thinking my arse was going to explode.
2nd, straightforward, the right way, walk in the park compared to 1st
3rd one, knew instantly i was back to back when i went into labour, hospital tried sending me home, i wasn't in labour, same as the first, i said no im back to back im staying here.
You are in a much better position as you know you are back to back so can prepare for it, don't let them send you home and you will be able to get pain relief. It's more or less what everyone else has said, be prepared for the pain to be in your back and bum. You will push for ages and it feels and looks like nothing is happening but it is.
I think its shocking how some back to back labours are send home as nothings happening up front, i know a lady who was back to back, same hospital, almost identical to my first and she delivered her 1st child at home in the bath as nothing was happening up front so she couldn't be in labour...go home.