Is it time I stopped working?

I am almost 26 weeks with my 5th child. Baby is measuring 29 weeks and needing to go for constant growth scans as i have a history of large babies (10lbers). I work part time at a grocery store and as a support worker. The grocery store check out chick job is surprisingly a lot more physical. I have excruciating hip and lower back pain after a 3 hour shift. With my previous pregnancy (2016) i had damaged my sacrum during delivery. Its near the tailbone. I now have sciatica. Whilst at work today my legs buckled from underneath me and i had to hold onto the cash register table thing to keep myself up. My boss gave me a fan and offered me water... theyre amazing in there but im just so sore. Im not really like it when im not working because im resting as much as i can. We do need the money but i just dont know if i can do this for another 12 weeks as planned