How do you deal with the anxiety, anger and frustration as an only child, caring for two divorced parents?

I am 51, and feeling dragged down by my mothers constant references to her ill health and daily dramas. Neither parent owns a home. My dad lives in a rented flat, my mum in a rented flat, but with semi care professionals around her. I live inbetween both of them, and travel around 50 miles a week vistiting each one. As any only child, I feel resentful now at 51, as my mum has been ill with nerves and various illnesses (some overexagerated) since I was born. Now at 80, she is genuinely in a bad way and in a wheelchair, with cancer, heart disease, diabetes, and dad sufferers with new illnesses now also at 80. Any ideas on keeping sane? I feel emotionally burnt out, as this feels like I have been worrying forever. Mum used to try and kill herself when I was a child, I have always had to calm her down, help her. I feel drained. much appreciated.