Struggling with new job after 6 months of job hunting

After 6 months of job searching I finally landed a job at a hardware store that didn't sound too bad. I'm in my first week and I've already had to take 2 days off due to health issues, including extreme muscle pain to the point I can move, throwing up, and generally high stress.

For context the store is still being set up and they have all the staff setting up the store moving items between pallets, shelfs etc. I wasn't aware that I would be setting up the store since in the interview the interviewer said they would be getting a bunch of university students in to do that job and I would be training at a different store until it opens early next year. After being hired they changed the plan and now instead of doing the job I was lead to believe I was doing I'm now doing a labourer job where I can't physically keep up. I'm not in the best of shape and originally I was looking for a job where I mainly talk to customers and help them since I enjoy that. It's going to be a couple of months before the shop is completely set up and given how I'm going so far I don't know if I'll survive until then.

I've started looking for another job but I don't know if I should leave this job before I've found another, not to mention the fact that the job market is completely shot atm. I'm trying to weigh up the agony I've had to go through trying to actually find a job vs the agony I'm experiencing in this current job. I'm afraid that if I don't keep up with this job they'll let me go and I'll have to spend another 6 months trying to find a job.

As a side note I'm also doing more hours and days than I agreed to, originally I was going to be doing 32 hours wed through sat. Atm I'm doing 45 hours mon through fri and its too much for me having gone from doing nothing but studying for a while to a full time labour job.

I'm also afraid to bring this up with those in charge since in my country we've got a just suck it up culture and I'm afraid they'll just say that I haven't got any options and end up with a target on my back.