I am not an expert by any means but I wanted to offer you some support. I too have lumbar issues. I just had a lumbar disectomy 3 months ago L3/L4 & L4/L5 I am also in alot of pain in the hip area as well. It definately can be back related. It can also be a few things. Having a baby is very hard on the body especially if you already have a bad back. Everything does get lax. Extra baby weight can put alot of pressure on joints causing them to inflame. same with discs.
You need imaging to see what the exact pathology is before you really can be treated afterall how do we know how to best treat if we do not know what the problem is??
Then a really good physiotherapist. I would stay away from chiro's. People with disc issues and so forth can be damaged even more by a chiro.
Also try antinflammatories if you are not breast feeding.
Aussie