Hi - can't find useful site.
However - yes it is very common. I had it very early on and MW didn't believe me - said it was too early (~4months), but it is quite common, as is SPD and other issues associated with over-lax ligaments!
Best thing for you to do is tell MW to refer you to a physiotherapist NOW, one which specialises in pregnancy ideally, to give you advice on how to not let the issue get any worse and also give you some simple and safe exercises to do to help. I think you can ease it by strengthening the gluteal muscles (I.E. your bum).
My MW didn't refer me until much later when I was obviously hobbling around like a cripple - and it was near Christmas so ultimately I never got to see anyone! - was due in the New Year.
Lots of luck and hope it eases up soon x