Hi Beth,
I am so sorry to hear that you are experiencing pelvic pain. However, I am happy to hear that you did seek medical attention and you are now having preterm labor.
It sounds like you are experiencing round ligament pain and maybe pubic symphysis.
The round ligaments are smooth, cord-like structures that attach to the top of the uterus and run downward, attaching again to the groin They are responsible for maintaining the anteversion (tipping forward) of the uterus. As the uterus grows they stretch and can cause sharp pain and discomfort. Round ligament pain is more commonly felt in the second trimester, but can occur anytime.
Because they attach deep in the base of the pelvis, they usually cause pain when changing positions quickly, especially moving from flexion to extension of the hips, moving from the horizontal plane (where they are not actively supporting the uterus) to the vertical plane (where they are suddenly called upon for support) and walking (where they have to support a constantly moving, jostling uterus).
There are some asanas that would be helpful. Those which bring the legs into flexion (squatting) or take the body into a more reclined position (supta baddakonasana). Generally, women who are affected by this are instructed to make slower transitions, allowing the ligaments to stretch more slowly and adjust more gradually to the added weight of the uterus.
As for the dull pain in your pelvis, it could be a separation of the pubis symphysis. (I actually just wrote a blog about this and ways to help the discomfort-
Pelvic Pain During Pregnancy) Check out the blog for poses to do and avoid. You may also want to get a belly band that can lift some of the weight of your belly and alleviate the strain on your pelvis.
I hope these suggestions help and you find comfort in the rest of your pregnancy.
Take care,
Deb