Lower back pain relief?

How do you relieve the back pain you get that shoots down the back of your legs? It’s so bad sometimes I can’t walk. Starts in my very lower back, threw my butt/hip(s), usually one side at a time, then down into my upper thigh(s). Rarely does it bother both sides at once. If there is anything I can do, what is it? Hot/cold hasn’t helped and it even hurts to sit when the pain is around.

Today I am 26w+1d