I remember in my last week or so at work (I worked til 37 weeks) I was constantly having to wee. I also had the feeling that I needed to either fart or do a poo - but when I got to the loo didn't actually need to. Does this sound like what's happening to you? If so then it's probably just the normal preparation as you head towards birth. I don't remember getting any pain with it though.

The tenseness & pain you are describing are most likely to be caused by BH but if it gets worse you might like to go home and take it easy. If the pain gets regular you might want to have a chat with the midwife.