Has anyone been told they have an irritable uterus?

After weeks of BH and my stomach being constantly tight for hours at a time, my doctor told me I have an irritable uterus. She said there's not much info or research about why it happens or how it affects pregnancy, but that it is common. She also said women who have this have an increased chance for preterm labor. Anyone else been told they have this? If so, how far along were you when it started & at how many weeks did you deliver?