Kitten, it need not get a lot worse if it's managed properly. Mine started when I was 13 weeks pregnant, the worst time for it to get worse is between 16-24 weeks when the relaxin levels are highest and you are safely past that part. There is some loosening of the pelvis which is normal (helps fit the baby's head through) but pelvic instability is where the pelvis has loosened far too much (too much relaxin or possibly preexisting looseness in those joints) and has nothing to do with when you give birth or how easy or not it's going to be.

If you see a physio they will be able to assess whether you're still sitting in the 'normal' range or not, and either way will have useful strategies. BTW I self-referred to the physio at the public hospital I was attending (free!), they have an entire staff of physios who specialise in women's issues and it's quite common for ppl to see them when they are pregnant. Don't be surprised if your GP dismisses it as 'normal' - they usually don't deal with this issue and often don't understand how painful or debilitating the bad cases can be. You might have to be firm to get the referral.