Sorry you're having such bad heartburn, Libbysmum!
I can empathize as I was getting that quite bad for 3 weeks. I think Tums became one of my major food groups! It would also wake me up at night and a few times I almost threw up because of that. Have you tried sleeping on 2 pillows to elevate yourself more? For me, that has helped ease it a bit. Also, my doc told me to try and not eat anything for 3 hours before bed, which is also helping....it's not gone but getting better.