Belly gets very hard - are these contractions?

Su

I’m 38 weeks and for the past week or so my belly will get super hard and stay that way for quite awhile. I haven’t really been able to time it or anything, sometimes it stays hard for up to an hour. I’m wondering if these are Braxton Hicks or if it’s just baby’s position that make it hard? It’s like solid rock hard when it happens so it’s slightly uncomfortable but not painful. I never got bh with my first so I’m not sure.