Im 30 weeks also experience it from time to time and glad im not the only one experiencing it. I really cannot walk fast or long period, sometimes even short distance i will get this pain. For that one is actually round ligament pain. And yes it can be very painful to the point i cant walk. There was once i even went to KKH urgent o&g for that. As for Braxton hicks, they are not painful, just uncomfortable. it will feel your uterus contracting like vacumm packed, then whole stomach will become hard rock and will last only few secs. Especially now in 3rd trim, baby’s growing bigger and heavier, so more prone to both ligament and braxton hicks.