Old injuries making work difficult

I started a job a few months back. I was in extreme pain my first couple of months, but then I thought I was getting better.

Then, my boss basically told me I wasn't doing a good enough job, and scheduled me for an extra shift every week, meaning I'd get only one day off. So... I pushed myself really hard today, and that turned out to be a really bad mistake.

I was in so much pain that I couldn't put much weight on one of my legs. I've been going to the physio therapist and she's pretty sure it's my SI joint, and I haven't really felt comfortable enough to mention trauma I received to that area, but she basically told me I need to look for another job.

I feel like it was a miracle enough that I landed this job. I'm kind of terrified to look for another one. But at the same time, I'm in so much pain every day that if I were to do the healthy thing and listen to my limits, I would leave. I just have such a hard time quitting, y'know? Feels like I'm just proving everyone in my life right.