sciatica pain at 38 weeks

ive had a pants weekend of vomiting severe back ache and generally feeling crap. all cleared up now apart from my back. got this intense pain just off the middle of my back which spreads round my left side. gets worse when i eat and walk around. yet the hospital are telling me to keep mobile... its so painful im in tears... im dreading labour anyone else suffering with sciatica?? had no show madam is 3/5 engaged cant take much more had enough now, which sounds awful but I've had a dreadful pregnancy from pretty much 5 weeks.