I experienced this in the last few months of my pregnancy. Definitely those hormones causing trouble! My bub was breech, and was nowhere near my pelvis so it wasn't pressure on my pelvis.
I also had a c/s, so can help you with regards to the birth.

The relaxin hormone can hang around for quite a while after birth as well, and I experienced pelvic and back pain up until a few weeks ago. Not as bad as when pregnant, but still quite uncomfortable.

I would recommend going to a physio. I just saw the physios at the hospital. I went weekly for the last 2 months, and it definitely gave me a little relief for a couple of days each week.