If i test positive for covid at home, does my employer have to let me stay home? i have an autoimmune disorder?

You have to isolate yourself for at least 10 days. You could be a spreader, and your employer doesn't want you at the worksite. Having an autoimmune disorder puts you at greater risk. Wait to you test negative before you resume activities.

Yes, quarantine is always needed, duration as established by local public health authorities, anywhere between 5 and 10 days and providing you clear your symptoms. Make sure you inform your physician(s) as well as your employer.