Sciatica pain

I'm 20 weeks with twins and haven't gained any weight just barely got back to my pre pregnancy weight due to losing 13 pounds Cus of hyperemesis gravidarum. Anyways I'm having horrible sciatica pain in my left side and I can barely walk I have to hold onto something with each step. Anyone else have it this bad? What helps with it. I bought a pregnancy strap to help with holding my belly up.