contractions

I've been told/read a lot about period like cramps during pregnancy aren't normal, but sense being pregnant I've had no other type of 'cramping' besides just that. No bleeding or complications at all I'm now 31 weeks and for the past couple weeks I've been having middle/higher back pain and not always, but sometimes here and there get period like cramps. More like the ones that feel like it's right in your actual vagina (don't know how else to describe)