I am 31 weeks pregnant and i'm getting period like cramps with lower back pain?

Timing is everything: Some contractions, occurring 1 to 3 per hour can be ok, if more frequent can still be ok, if baby is healthy and cervix is NOT changing. If 4 more per hour, and/or if baby is moving less than usual, you should discuss with doctor and likely be checked for preterm labor at the hospital. Irregular contractions are often called Braxton Hicks/false labor, and are considered normal in most cases.