I have retired friends who seem to need to have a plan for every single day, whereas I view a week with little pencilled in on the calendar as a real treat!
The loss of purpose feeling takes a while to get used to, (oh the guilt that you could be achieving so much more!) but the lovely thing about retirement is , you can be as busy or as idle as you please. Never in my adult working life and role as a single parent have I had the luxury of idleness - so I absolutely relish it in retirement. Time which you enjoy wasting is never wasted time as far as I am concerned. But we are all different.
Looking at your OP lippyqueen it seems you have quite a lot going on in your life - you look after your grandchildren, dog, you walk, garden, keep fit and have the care of your mother to see to. You write that you lack contentment.
It's difficult to advise you because we all find contentment in different ways. It could be that you (like I did at first) feel as though you still have more to give, that you are not 'used up' yet, in terms of energy and giving, being needed? It could just be that you haven't yet fully adjusted to being your own boss now, maybe. You don't have to be always busy any longer, and you can pick and choose to a certain extent how you spend your days. You do sound quite busy though.
I can only say, enjoy that morning coffee, the crossword, the lazy lunch, the times you can decide to do something, or nothing. If you have your health and strength all the better. Perhaps you need to join things so you have classes or activities to look forward to that get you out of the house, somewhere different and challenge you?
I do hope you find contentment soon, although your mother having MND must be a worry and a sadness. It could be that which is a sticking point.