Sounds exactly like what I've been feeling. I think my belly feels tighter if I've been really busy and on my feet a lot, which could be why you feel it more at the end of the day?

Definitely normal to be getting BH. Apparently I was having one during my 20 weeks scan. The sonographer said that the lower part of my uterus was thicker (or something like that!) than usual, which was probably caused by a BH.

So many weird and wonderful things that happen to your body during pregnancy that no-one warns you about!