damn my back hurts

Tegan • Australian • Taken • Mumma to 1 •
So I'm not sure if it's anything to be worried about but since yesterday, I have been getting back pain. Now, yesterday, the back pain came twice and was there for about 1 minute. 
Today, the back pain started at around 3PM and came once and was there for about 5 minutes and it has since been coming every 30 minutes and staying for about 2 minutes and than going again (it's 8:30pm now). The pain is in the middle of my back. It's probably nothing but I am a FTM and I just think it's unusual that they are coming and going. Should I be concerned? I'm nearly 27 weeks by the way.