That is not nearly enough. I worked 6 days/week (no stall cleaning), 10-12 -hr days and in addition to pay, got a small studio apartment on site, board for one horse, and lessons with the owner whenever they were home between shows. I got paid the amount you’re getting, over 20 years ago!!!
I did get somewhat burned out, but did love the years I spent there. I did end up switching to a non-horse job, getting my ammie status back, and now I love life a lot more. As others have said, you need to think about long term security, because it’s not realistic to be doing what you’re doing now at age 60.
When we have barn help, we pay $15/hr. I think even if you generously count the living space value, you’re making much less than that.
Personally, I’d ask for a significant raise, enough regular time off to hold a second p/t job, or walk away.
Think about why you’re doing what you’re doing? Is the current position helping you attain long term goals? If not, what can you do that would help you down that path?