Hi there

Sounds like you have an unstable pelvis - it's also called a lot of other things. There's an article on Belly Belly about it, under I think SPD.

GPs are hopeless at diagnosing and treating this. You need to see a physio - depending on how severe it is they may give you a belt or exercises that you can do. Try to see one who specialises in pregnancy-related conditions.

It usually goes away after the birth - don't worry too much about the actual birth, it won't really impede it but there may be some positions you can't use.

I got it at week 28 and it only got better six months after the birth with clinical pilates (it's rare that it takes this long though) so I know that it can be absolutely agonising and believe me, putting up with it for that long was far worse than the actual labour!

Take care and get thee to a good physio!