Am I going in to labour ?

I think it could be contractions, but its more in my back/bum than stomach. The pain is really soar and only lasts around a minute goes and comes back about 8 - 10 minutes later it only started an hour or so ago though. My baby's in breech & I'm supposed to be having a c-section on the 18th(next Friday) at 37 weeks & 1 day. I have phoned my boyfriend and he is on his way home from work but should I call the hospital or leave it for another few hours to see how it goes? Midwife hasn't gave me any advice on this because she didn't think I would go before the c-section, any advice will be much appreciated. Thank you xxx