What can I do if my mother's family doctor refuses to believe my mother requires constant care?

I'm in what I hope, since I wouldn't wish this situation on anyone, is a somewhat rare situation. My 77 year old mother has gone, over the course of months, from relatively self sufficient to so demanding of me, as her live in caregiver, that I have not a moment to myself to so much as even to sleep at night. She is rude, agressive, prone to temper tantrums, moderately incontinent and has multiple, serious co-moribund conditions, including renal failure and a platelet disorder. Her short term memory is failing and her attention span is poor.

She has been hospitalized four times in five months; once for “lack of care” (she had, while I was still under the impression she was eating, taking her meds, etc, begun spending all her days in bed, starving herself and neglecting her medical care while I was out), the second time for heart failure, then pneumonia and, most recently, confusion, weakness and an expanding aneurism. This latest hospitalization included two weeks out-of-province, the bulk of which was spent waiting for a bed in geriatric rehab to transfer her home to.

The nurses who treated her during her brief stay in rehab and out of town knew she was hallucinating and paranoid.
The geriatricians who assessed her saw some concern.
Several care professions have suggested Alzheimer's as a potential explanation for the personality disturbances.
The extra mural staff who have been visiting us are concerned for her health and my stress levels (I am with her 24/7, have had to give up all my activities and friendships).

Her family thinks she's fine.
Her family physician thinks she's fine.
She tells me, and anyone who will listen, that I'm the crazy one, I'm making it all up, I haven't done anything for her, I haven't been there at all.

Her doctor, after letting me run myself bankrupt staying out-of-province with my mom, waiting for that bed in her home hospital, decided to send her home immediately upon her arrival, declaring her "fine". Why he put me, not the mention the other hospital (which had to tie up a much needed and expensive bed and send her back by ambulance), through this when he had no intention of following the recommendations from the geriatricians who assessed her is beyond my understanding...but maybe this is a common situation after all?

I'm in my 30s, single and childless, now unemployed and beyond miserable. As the late-in-life only child, I feel a sense of duty, that I have to be there, to be at my mother's side when she dies (as I was for my father, who ate up a chunk of my 20s), but yesterday I hit my crisis point.

I don't want to be responsible for my mother's death, which is exactly the position I've been placed in. I can't afford to pay for her care right now (she can pay for it, but it would take all her money on what is, when you come right down to it, my responsibility) and if I leave her, she'll die of neglect. If I stay, it's impossible for me not to trigger her rages and crying fits, during which her blood pressure goes up, which has already had a dire consequence. Her per-existing, triple aortic aneurism grew while she was in my care during December and January. It is now unstable, basically inoperable and could burst at any time.

I'm on the verge of burnout, if not nervous breakdown. I'm very concerned that my mother's not receiving help she needs because her doctor doesn't take me seriously.