Mama, please check with your OB agad about this pain pattern, lalo na at 31 weeks ka na, mas better safe than sorry when it comes sa cramping and lower body pain during twin pregnancy.
Twins can definitely put pressure on your belly and back, pero ang pattern mo ng pain coming and going with their movements ay importante i-discuss with your doctor to make sure lahat okay, especially since you're in the third trimester na. Maraming twin moms dito sa community, so I'm sure marami ring nakaexperience ng different things, pero your OB pa rin ang best person to explain what's normal for your pregnancy specifically. Hugs, mama!