I had the constant period pain with hard belly for 2 days before DS was born and had no idea it was early labour. It didn't get worse, it was just always there and then my waters broke and things got started properly a few hours later. As for the tummy being hard, mine's like that most of the time at the end with both DS and now with this one... there is simply nowhere left for bub to go. I think you should definitely call the MW again whenever you're worried - that's why they're there. As for the plug, that can happen a few weeks before giving birth and all the prelabour stuff can too. Good luck though, hope bub stays put a little while longer for you.