Hi 2196 Alexandra
I'm sure the help and support line top left line can give you some signpost as to what to do next whatever your fathers illness turns out to be. Another thought is Age UK at http://www.ageuk.org.uk/
If you go on to the site it automatically picks up on where you are and leads you what's available in your area but first I would try the free helpline for information 0800 169 65 65.
I hardly dare put into words how your GP is letting you down. I am 73. 67 is not old by todays standards (the government is raising the retirement age to 67 etc.) even if we are in the NHS geriatric category and in my humble opinion you don't go downhill this fast with so many symptoms without a cause beyond old age. Is there not another doctor at the practice or is it just him? It is difficult when you are acting on someone else's behalf but would your Dad have enough insight to agree to changing doctors. It was only when my mum's leg swelled up to three time the size and cracked because they used penicillin power on a tiny break in her skin when she had repeatedly told them she was extremely allergic to penicillin that at last she agreed to change to a different GP Surgery. And my father had been given mouth wash when he couldn't swallow and turned out to have throat cancer. Some people are simply bad at their jobs including doctors. Be confident in the fact that you are the expert in how your dad was and don't be fobbed off.
A lot of your father's symptoms are associated with PD. It affects people in a myriad of different ways and 30% do not present with a tremor but whatever it is its not usual at 67. Most doctors will agree that they do not know much about PD.
I was told by the very nice hospital Geriatric Consultant my mother probably had about three months to live and she lived nearly ten years longer to the age of 99.
You are also entitled by law to a Carers Assessment by Social Services whether the person you care for agrees they are ill or not. However, like a lot of things it goes by and by in some areas. If you are assessed it could help your situation. A lot of people resist being identified as a Carer because "he/she's my husband, wife etc" but you are an informal carer and entitled to consideration and respect.
I have gone on a bit, perhaps because I am secretary of a carers charity and "hidden carers" are a big area of concern.
All the best and look after yourself