I quit work when it became all that I could manage to do with my life...go to work, come home, crash into bed, get up, go to work. Sounds like that's the situation you are in.
Unfortunately, the way the SSDI works, you probably should have applied long ago, when you were working more hours, as how much you will eventually get (assuming they approve your application) is based on how much income you had in your last 3 years of working.
At any rate, before you quit, consider these things:
Have you worked long enough (and paid into the social security system) to even be eligible to apply for SSDI? You can simply call your local social security office, give them your name and social security number, and ask. They'll be able to tell you whether you're eligible, and approximately how much you might expect (make sure to tell them you have minor children, as they might get some $$ too.)
Also, you mentioned financial problems...if you and your family are low-income (VERY low!) .. you might be eligible instead for SSI..supplemental security income. You can also ask about that when you call the social security office.
The injectable meds (you didn't mention which one you're on, but it doesn't matter) aren't designed to help with symptom relief. You could ask your doctor about getting on some meds for fatigue, pain, and other symptoms, which you'd take in addition to the disease-modifying drug you're on.
Many folks who struggle with MS related symptoms find their symptoms greatly reduce and their health improves significantly when they're not under the stress of having to maintain a job. Yes, the finances certainly are an issue...but depending on your husband's employment situation, you may be able to find a way to work that out without continuing to jeopardize your health.
...I am not a doctor, nor health professional, and don't pretend to be one, here.....