Iliac crest and lower back pain post pregnancy. doc wants to do pelvic exam and pelvic ultrasound. does this make sense? doesn't seem related to me.

Unsure: I would not normally think it would be related to anything that would show but they may have seen something on other exams they are looking for such as fibroids, endometriosis, or adhesions and they just want to rule out more serious issues first and then look at musculoskeletal pain after that. Ask them frankly and they should clear it up. Hope that helps!

Unlikely but yes: Although it is more likely that the ligamentous laxity from pregnancy is causing your back pain or that you have a particular anatomical cause of back pain, pelvic issues certainly can be a cause and should be checked out initially.

Possibly: Your doctor is trying to rule out a pelvic cause for your pain, which can radiate to the back as well. If this does not give you answers i would suggest seeing a spine specialist to see if imaging studies might be needed to figure out why you hurt.

Yes: This makes perfect sense as an exam to rule out any obvious pelvic pathology which can create low back pain when there is actually nothing wrong with the back. Your doctor is being thorough and i would agree completely that this is a good starting point.