I've run some numbers here.
So prior to your husband getting ill, it was just him working (you SAHM), obviously for 100% of salary.
Then he got ill, and went down to 50%. You got a minimum wage job at some stage in this, to top up the income.
Then you got ill, can't work, so your family income is now your PIP and his 50%?
Your income (presumably after tax) is 2500. High rate pip is £778, so his 50% pay must be 1772 roughly. When you were on minimum wage (presuming full time), your joint income would have been slightly higher than when you were a SAHM.
From where you were comfortable to now, you've got a shortfall of about £800 to make up, from what I understand it? Though to fit in your stated incoming you need to find about £330.
Whilst thats possible to squeeze by reducing your overheads (those packed lunches again, getting rid of a car, reducing food bill etc), the most practical option might be to look at creative ways of earning more. It depends on the nature of your disability obviously, but some part time remote earning could plug that gap. Or as others were saying, carers allowance. Or both.