if you haven't had sciatica before, chances are it's SPD/PGP (symphysis pubis dysfunction / pelvic girdle pain)
"PGP is often misdiagnosed as sciatica. Only a few women, just one per cent, have sciatica during pregnancy. We now know that most lower back or leg pain in pregnancy is PGP (Ostgaard et al 1994). "
great article with some tips to help
https://www.babycentre.co.uk/pregnancy/antenatalhealth/physicalhealth/pelvicgirdlepain/
I find swinging my arms while I walk helps the pain in my hip, and keeping my legs together as much as possible seems to help with the pain in my pelvis - not 100% but better...