The stress and unvarying inactivity of being a caregiver (if you take care of ailing parents) makes it hard to feel in control of your weight. I took care of my ailing mother and gained weight - even though I was only eating one restaurant meal a day. I realize restaurant meals are caloric, but come on!
I was reading a study recently in which they MADE people gain weight by slowly DECREASING their daily activities and increasing their calorie intakes.
Changes in insulin sensitivity precede change... [J Appl Physiol. 2012] - PubMed - NCBI
They had their steps counted and they were slowly reduced in number of steps they could take. They got slowly less active. They gained weight, surely as anyone could have predicted.
I have been taking a class which requires a lot of study. Every day, I have some test I'm preparing for, or some report I'm preparing. I wear a pedometer all the time (I have been losing weight on Weight Watchers and they encourage walking at least, with step goals, etc.) and I've seen my steps reduced to a quarter of what my daily step count usually is. No surprise, I've also seen my weight loss slow way down, and I've had to work harder at reducing my calorie intake.
One thing I can suggest is walking in place to any walking tape by Leslie Sansone. You can walk indoors, in place, taking up very little space and very little time. I believe the entire taped 'walk' only takes 20 minutes or so. It won't make the weight fall off - although for some people, it has made some dramatic changes when they changed their level of activity - but it's one way you can feel you are building protection against even more weight gain.
I have a Leslie Sansone video tape somewhere, but it's available also on DVD. If you go to iTunes, I'm pretty sure there are mp3 podcasts you can download and listen to while you walk (in place, if you have to stay in one place).