It's been a few days. Thanks for all the replies.
A lot of the stuff people suggest, I'm already doing. Like eating whole foods. I eat almost no multi-ingredient foods. I'm pretty much gluten-free, since gluten gives me dizzy spells. I eat a bowl of oatmeal (not instant) each day, but that's it for grains. I eat chicken breast, fish, and canned tuna, either with steamed veggies or veggies cooked with a bit of olive oil. Most days I have lowfat cottage cheese with canned fruit. Another food I eat most days is a rice cake with natural peanut butter. The one place where there's room for improvement is that there's also a little bit of chocolate in my diet, and a hard cider now and then. Not every day, mind you, but once or twice a week. Enough to account for about 400 calories of my weekly total, these days. If I replaced those with a plate of steamed broccoli, that would be much more impressive, but I'd be a miserable weirdo who has broccoli when she could be having a cider.
No soda, lots of water. I eat out about once a year these days. No Starbucks.
As far as weight training, I'm doing only major muscle groups. Not triceps kickbacks for me. I do squats, pull-ups, and push-ups. That kind of stuff.
So, I don't know. Since starting this thread, I've gained another pound. I have started doing more cardio, and bought a heart rate monitor so I can work at an appropriate intensity.
Maybe I really do maintain at 1700 or so. I guess people do. That would explain why I gained weight so easily. I've never been a junk food eater, although I used to eat a lot more bread and a lot less meat.
Oh well. No one said life was fair.