If it continues consistently I would go to the hospital.
My sister started with back labor early and when we decided to finally take her to the hospital she was already dilated to a 6, they were about 3-5 minutes apart consistently.
I had back pain at 24w with my daughter...went to the ER and wound up in the hospital for a whole month...till 28w. i was dialated 1.5 and 60% effaced. i was on strict bedrest from 28w till i gave birth a few weeks early...back pain can mean cervical changes...better safe than sorry...if your worried...go get checked...good luck :)