Prob stupid question- rock hard belly

39 weeks and belly has felt rock hard all day long. Seriously like one long braxton hick..no breaks in between just one long continuous TIGHT belly since this morning. My back feels seized up. I rested for like 2 hours on the couch, literally doing nothing but kick my feet up and drinking tons of water, expecting my belly to soften but nope. Rock hard belly. Normal? What happened?