BH is tightenings of the tummy. Feels as though your tummy is squeezed very tight and will feel uncomfortable but should not feel any pain. Comes and goes and normally will subside when you change your position.
While contractions in the other hand is painful and will get very intense. Pain will not go away no matter what you do & it normally starts from the back to your tummy.
BUT do have a check. I just gave birth and before that I kept having what I thought was braxton hicks cos I felt no pain but only tightenings although frequent. Turns out I was actually having contractions.