SIJ that Clarebear mentioned is PGP but just with a different name.

If it is PGP/SIJ you could have it right up til 12 weeks after giving birth but this is unusual, usually it goes away after the birth. I read somewhere that a lot of women get this during their pregnancy - some just get a few days, others weeks, some get it right through. Some women get it mild, some get it severe.

I could never work out if it was sciatic pain or PGP that I had when I was pregnant as it felt very like the sciatic pain that I had pre pregnancy (and post). I got a few days of pain early on & then a fair bit of it during the 3rd tri but it was never unmanagable.

Pelvic floor excercises are thought to help with PGP so if you aren't doing them yet get to it quick smart.