Suggest Treatment For Pain In The Spine Which Radiates To The Back

I have had a throbbing pain that starts a the bottom of my spine and works its way up my back, I have had this on and off over the last month however today it has been all day, can't say its happening at regular intervals but it takes my breath away and I feel that I can't move. I am 39 weeks pregnant and midwife today said I was 3/5 engaged - could I be in labour?