Hi Julie and welcome to the forum - by the way we don't call it 'whinging' on here - we 'let off steam'
: lots of it
My Mum had dementia and I cared for her 24/7 for the last 3 years of her life - sadly she passed away in March this year. It's very hard caring for a parent when the roles become reversed and in effect they become the child and we become the parent.
The best pieces of advice that I can give you are:
1) Contact your local Alzheimer's Society group - the support and advice they can give you is invaluable.
2) Come hell or high water make sure you get some proper time (half a day at least) to yourself every week, plus try to build in an hour or so each day as well.
3) Check with the Carers UK Advice Line that you are getting all the support and benefits that you are both entitled to. (contact details are here viewtopic.php?f=4&t=18890