What I want to do in the evenings and at weekends is grab a cup of tea and snuggle down in front of the fire with a re-run of Wycliffe. The last thing I want to do is write. Creativity and tiredness are not easy companions. But. But. But. Tiredness can also be an excuse. Most of us are tired, but if you want to write you have to find the hours when you can.
I had two young children when I wrote my my first novel and to be honest I don't know how I did it. I remember getting up early, staying up late, writing while dishing up supper (watching out for spag bol on the keyboard). I wrote that first draft while my busy life carried on around me. Tired? Yes, of course, but the motivation to write kept me going.
It's always the first ten minutes that are the hardest. Once you're underway, the writing warms up and soon an hour has gone by without you realising it. And by the end of that hour it strikes you that a) you don't feel so tired and b) you feel proud of what you've achieved. You pushed through the tiredness and now have something to show for it. Hooray!
So forget the tiredness: you'll never get anything done if you wait until you feel fully refreshed. Just get on with it - even if it's only for ten minutes - and enjoy the glow of achievement when you've done some writing.