Hey Fiona. Maybe it could be a good idea to get a referral to an endocrinologist?
I think relaxin has many roles both during pregnancy and otherwise: not only to relax the ligaments of the pelvis. It's also a vasodilator and therefore affects bloodflow, blood pressure and kidney function.
I am sure there would be medication to regulate this hormone, (I think there is relaxin treatment available which increases the level of it in the body for cardiac problems, but not sure about decreasing the levels) but not sure if that would 'fix' the issue anyway? Haven't done much reading, but I'm sure there'd be stuff for you to investigate online.
As for natural therapies, I have no doubt there'd be something your naturopath could recommend to try to regulate hormones, but I've no idea how effective it may be.
Best thing would be to talk to someone who knows hormones.