I can really relate to this....
I feel like such a slob, I don't even work full time anymore and I still have trouble finding motivation to clean and tidy..
I like the timer idea, thanks for that idea, I'm definitely going to give it a go.
I find personally I make jobs out to be much more difficult than they really are, for example getting out the the vacuum cleaner and having a vacuum seems like such a huge chore but when I actually get up and do it I find it's over in 20 minutes. And I feel like I've accomplished something when it's done.
Please Don't be so hard on yourself, you are working long hours and coping with a dog, of course you will be tired after work everyone is.. and after all is a spotless house really that important or realistic?