I had sciatica before pregnancy and bought a knee pillow (I've got the slumbar pillow) and it makes the world of difference. Only time it came back really was when I stopped using it and tried switching to a pregnancy pillow. I also find my birthing ball helps with the pain if I do gentle rocking and figures of 8. Definitely refer yourself to physio. Usually they'll see pregnant women much quicker. My physio gave me a belt for when I'm doing longer walks etc.
I had it and had to go to the ED because I was in so much pain, literally could not take a step, they gave some painkillers and said it won’t go away and it’ll get worse as the baby grows. But, I came home and got a pregnancy pillow and a pregnancy belt, also started with some small stretches which I found on YouTube for sciatica and started doing walking. I don’t know which one helped but I don’t have that pain anymore or it’s verrrry dull if I do feel it sometimes.