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Try sleeping with a pillow between your legs, that can help a bit. Tomorrow when sitting, put a rolled up towel in the small of your back. Things to try are a tens machine if you have access, pain killers from doc, along with creams to rub in. It's an awful thing to have, but I hope it will soon go away for you. Also do not sit for too long at a time, about 15 mins then a little walk around.
Hot water bottle and then something frozen... alternate them. Ibuprofen helps. Then try osteopathy and when able do yoga to prevent it...I have had sciatica years ago and now with yoga no issues for years.