Hello. 28 weeks pregnant, belly is getting smaller for the third week …

Hello. 28 weeks pregnant, belly is getting smaller for the third week now, there's no pain or pulling sensations, only it's getting smaller and heavy. The cervix shortened, they want to put in a ring. It gets smaller mainly when I want to go to the bathroom and at night. They're treating uterine tone, but based on characteristics, it seems like training contractions. Can you please tell me what this really is?