Diarrhea like cramps

28 weeks with twins and seems like on and off for the past week that I've been getting what seems to be diarrhea like cramps and at first it would go away after I went number two. But the last couple times I couldn't go to the bathroom I would just pass gas and it would go away. Is this just a part of pregnancy? I've hear so r some women it's a sign the body is preparing itself for labor. P.s. I'm a first time mom and it's twins. Any advice?