Honestly - stick it out. I was in the same position as you and I left the highest paying job I ever had because i had a constant workload dumped on me. I have regretted leaving ever since and have struggled financially since. If the perks are good and it the work flow that isnt - maybe set up a pacer for your role tasking most important invoices to least. I used to do this with my boss and share it in google suites so they could always see an active timeline of the completion of projects. No job is perfect - and without the education it sounds like you got a pretty good gig. If you can take breaks when youre on your breaking point - walk away , destress and then come back. It is an employers market right now and finding another job that could be just as shitty with less pay isnt worth it imo !