As a 31 weeks today pg and not a health professional, my gut instinct tells me to give your MW a ring and tell her, she might say its OK to leave until 3pm or she might think its best that you pop to mat ward.
Eitehr way, you'll be reassured that you've taken her advise IYKWIM.
Glad everything is OK now. Hope you can relax for the rest of the pregnancy.
I ended up with nasty BH and crampy feeling in my back too yesterday. It lasted about 4 hours before going off. Had to wait for someone to take DS before getting checked out and by then it had stopped. MWs said no need to come in... they are so much more relaxed when you've already had one baby.