The girls is bothered by a hard belly, it started at 2 trimesters with…

The girls is bothered by a hard belly, it started at 2 trimesters with ultrasounds everything was good, then so not worried about it, read that the uterus starts to contract from 3 months and some feel it and some don't type and calmed herself down...but now it hardens often and presses on the bladder more because of the low position of the baby... but the belly doesn't just harden but like a balloon inflates for a minute then normal and there's no pain really, rarely shows up when the intestines are bad, went to several ultrasound doctors all say that there's no tonus more likely due to anxiety and etc, gynecologist didn't pay attention, she started taking magnesium... anyone