Ruby, I do the same as you do: I walk the dog once or twice a day (dog always gets 2 walks but most of the time I force dh to do the evening shift - for his benefit rather than the dog's) and do sit-ups, press-ups, weights etc as and when. I've been doing circuits for 18 months now and wouldn't have done it unless I was enjoying it, but have suddenly started not enjoying it so much. I am the oldest in the group, but there are some extreme fitness types in their early 40s who are beginning to make me feel really bloody decrepit. I was competing with them, but as of last week suddenly can't be arsed any more. It was a "20 press-ups, 20 star jumps, 20 burpees, repeat 3 times in x minutes or get shouted at" that suddenly caused me to turn. Also the realisation that I seem to have developed an "I've burned it, I've earned it" attitude that means I'm probably eating more than I used to. 
Time for a change to doing something else, probably.
BTM, oh to be lying in the sun .... :)
It's bloody freezing again here and I am taking ds, dog and a bunch of friends to the woods this afternoon. Brrrrr. Dh is in a big, fat grump because he has once again cocked up on the time management and is up against it with 2 deadlines. He is of the opinion that I should suddenly magic up childcare and help him out.
Now dragging limping dd off to get her eyes tested. Am a bit worried she may have become short-sighted and am not looking forward to the whole fucking drama if she turns out to need glasses. Her life will be as good as over, apparently.