Hello,
It may be related to the increased laxity of the pelvic bones due to the pregnancy. Have your ob or midwife examine you at your next visit.
Best regards,
Dr. Downing
Not sure about twins, but my sencond child was way, wasy worse than my first. My hips spread so far out about 28 weeks, it was like i could even feel the ground beneath me. I was a cluts, with know balance and always sore. I am sure i has to be worse carring two childern. Good Luck and Best Wishes.