Period like cramping

What causes period like cramping at 28 weeks? This is my fifth baby and you'd think I would remember, but I don't 😑 I'm very much lacking on energy anyways (thanks 3rd trimester) but then when I get up to do a task, I'm hit with instant back ache and period like cramping. I don't believe they are Braxton hicks. When I get BH I feel everything tighten and then release....this is just all over cramping just like my period. I'm assuming just my body growing/preparing for what's to come? Any insight would be great!