Getting pregnant with pelvic instability

I had really bad pelvic instability during both my pregnancies. The first time it started around 28 weeks, and the second time as early as 20 weeks. The second time, I could barely walk at first—only about 100 meters. Around 30 weeks, I could barely sit without pain. The second time, it went away immediately after giving birth (or maybe a week later), which was a pretty quick recovery.