Cramping at 35 weeks

Hey everyone,

I'm having some lower back pain and period type cramping every half an hour for the last few hours. Past few days I've had a couple others but nothing regular until tonight. They're not excruciating, just like mild cramping, but just made me nervous given that they're more regular tonight. It's outside of office hours and I know the answering service will always say to go to L&D, but I don't want to go for them to say it's nothing and I'm being silly. Anyone have any ideas?