Sorry you're going through this A.! I had the same issue with my son starting around 18 weeks :(
Try icing the middle of your back (not down by your butt or hip where it hurts, but the actual middle). Sciatic nerve pain comes from the nerve being squeezed by all the other stuff that's crammed in around there and a little ice can really help.
A belly band also really helped me. Seems silly, but it really made a lot of difference.
Make sure you're in good shoes.
I found that any stretch that made me feel better right in the moment (the ones that make you say "yeah, right there") ended up getting it all revved up in the long run. Do the recommended exercises each day, ice your back throughout the day and hope your growing belly knocks something back into place before March :)
Hope this helps,
T.