I'm wondering if you just aren't eating enough. There is nothing wrong with grazing throughout the day, but what you are eating doesn't seem like enough calories given your current weight. Have you tallied up what a usual day looks like calorie wise?
By my estimation, you are only eating around 700 calories before dinner (although I'm not sure about your serving sizes--so this could be wrong.) I'm not sure how much you are getting in your dinners, but since you say you eat small portions, I'd say not enough.
The thing is, that to keep your metabolism up and running, you need to eat. You just want to make sure you have a calorie deficit so you lose, but you still need to eat a decent amount. If your body thinks there is a famine, it's going to hold onto to everything it can.
I was close to your current weight when I started and I was eating 1700-1800 calories and lost approx. 2lb a week. I never tried to go below 1500 calories per day.
Maybe you should look into calorie counting and eating more? I do agree that more protein and more fiber are in order, but I really think more calories may be needed too.
As far as working in a windowless environment, maybe you could talk to your boss about having full spectrum light bulbs used in the office? I'm sure if you did some research you'll find studies that show these types of lights help productivity too. That'd be a good way to bring it up at work.
Exercise is important for health and weight loss. I think getting it in anywhere you can is a good thing. Maybe before or after work? Regardless, of whether it helps you lose or not, it'll make you feel good and will make you healthier.
