Long periods of painful cramping at 37 weeks

I keep having multiple hour stretches of painful, period like cramps sometimes including bad lower back pain. Yesterday was about 5 hours and this weekend i had it for about 30 hours straight. I get lots of braxton hicks during these pain sessions, but the peak of the cramping pain isnt always aligned with the tightening, and sometimes the tightening is lasting 15-20 minutes at a time. It drives me crazy cause I keep thinking it is early labor, but it never forms a clear pattern. Also there are no breaks like you would have between contractions, just constant pain that gets more or less intense. Anyone experiencing this? Is there something wrong or is this just my body starting to prep for labor?