Back aches and working

Hi im 23 weeks pregnant. I started have bad backaches and its below my left hips . Literally at the bone below my hips that i can barely moves or my leg with give in. Currently working as a cashier and requires long hours of standing. Sfter work the pain worsen and even when i lie down i cant put any weight or force to my bottom left.. anything can help with the pain? I put on some oil and self massage but not getting anywhere close to better?