Good to check with MW for reassurance. I have been having practice contractions since about 30 weeks (as have all my NCT class). Mine feel like my bump has gone really hard for a few seconds. I get the lower pain if I have been walking a lot usually.
I got this through both pg's. Worried myself daft both times. Nothing was the matter and apparently it is very normal, all to do with stretching and moving babies. Run it by the midwife but I really wouldn't worry too much
It's probably BH. You only really need to worry if the pain becomes regular to the point of being timeable and doesn't go away if you change what you are doing. Or of course makes you start looking for painkillers every time.