Dehydration or BH?

28 weeks tomorrow and since around lunchtime yesterday, I will get these excruciating, aching, period-like cramps in my lower back/hips, but on the sides. They aren't consistant like what I assume contractions to be, but they last about 5 minutes each time they come. I have never been pregnant so I don't know what BH or real contractions feel like, and I've been told your muscles can ache from dehydration when pregnant-- I don't drink water at all really, but I feel I definitely drink enough fluids to not be this dehydrated, and I don't have any other symptoms of it. I've posted a photo below indicating where the "cramps" happen.