ImpossibleBlonde, you are trapped in this vicious circle by your own fundamental good nature. At the moment you are also ill and exhausted, not least because you don't have a proper bed to sleep in. I hope your hospital appointment was some help in sorting out your medical problems.
You need to assess your situation by asking yourself:
do you have any independent income; are you in a position to work and earn money; is there anywhere you could go to escape this situation and support yourself? Do you have any stake in the place where you are living or are you dependent on your partner? You are trapped in four walls now, plus all the unpaid caring you do for his mother.
Your partner is a dangerously selfish man, who is happy for you to sacrifice your bed, home and health to the needs of his mother, (whilst doing precious little himself) yet has so little respect for you that he harasses you when you see a male doctor. Social Services won't come to your aid because his mother can and has refused their help, and your partner doesn't want them to, probably because of the cost; ultimately the mother's house would be sold to cover costs if she moved into a home.
Concentrate on getting your health back and don't be so foolish as to discharge yourself early if you are hospitalised; use it as a chance to rest. Then plan for your future.
It won't be easy and don't underestimate the power and iron will of this woman, but the situation will only get worse and you will pay the price.