Constant hard belly.. normal?

39 weeks exactly, FTM. Since about noon yesterday I've been having contractions on & off. Nothing constistant or painful but they're definitely extremely uncomfortable. Lost my mucus plug early this morning (or at least some of it) that was followed by light brown discharge that stopped a few hours ago. Anyway, since I started having contractions my belly has been hard. Not rock hard like it gets with the contractions but it hasnt softened up like it was before they started. Is that normal?