I suffered from horrendous back pain during and after pregnancy. It gave me grief on a regular basis until I stopped breastfeeding - sorry, I'm just bring honest!!

I still see a physio who specialises in pregnancy and post-preggy issues (I do pilates with them weekly). They've been amazing! I had a dodgy back before I fell pregnant so it was no surprise it played up during pregnancy however, I didn't think I'd continue to experience pain well into my first year as a mum! My physio thinks the hormones were still harassing me during breastfeeding which could well have been the problem as it was amazing how much better my back felt once I stopped BF DD (I wouldn't have stopped BF to test that theory though). I still get a few odd niggles in my lower back but they go as quickly as they came

Pelvic floor exercises do really help as they strengthen your core muscles, the source of lower back pain.

HTH!

PS I wore DD in a sling a lot when she was little but it was my lower back that was the issue most of the time so in my case, I don't think it was really related.