Whats the difference?

Any moms out there that can explain the difference between BH contractions and regular labor contractions...of what they feel like? I know that BH contractions are like menstral cramps, your belly gets tight, more uncomfortable than painful. Are labor contractions the same sensation but you have sharp pains in your belly? Is that the only difference is the pain level? And does labor just come on strong out of nowhere or does it start and gradually get more painful. Everyone says, “you”ll know when its the real thing”. I know what BH contractions are and what they feel like but I’m starting to get sharp pains through my belly as well which is new. Just curious of what to look for. Thanks! Will be 39 weeks tomorrow.