I agree with Sally, trust your instincts! If you feel any twinges/back aches around 35 weeks go to the hospital to be checked. They won't mind, I was going three times a week in the end to be monitered. I had a checkup on the day the meds finally stopped working and my cervix was still closed, it all just progressed really fast laster that night.

I didn't know I was in labour either with DD1, it was only when my waters broke that I realised I had more than a sore back!