I am no medical expert, but I do suffer from depression as we speak and I am taking medication for it, which really helps.
A long time ago, I had problems with gaining weight after the birth of my second child. It was definitely stress-related. You see, at the same time, my husband was being treated for cancer with a 40 percent chance of living. (He lived.) But I was and I was caring for two young ones in diapers and a very sick man full-time, with no time to breath. Even after we were in the clear, my routine didn't really slow down. I look back now and believe that it was post-traumatic stress disorder, but they didn't have a name for it back then. I have experienced this phenomenon two more times since then, once recently.
Anyway, I was already a slim person, but when the cancer went into remission, people began to comment on how much weight I had lost and how unhealthy I looked. It wasn't the normal, "I'm jealous because you're thin and I'm not." So, I tried to eat more, but I couldn't seem to gain it back. Just eating larger portions wasn't doing it.
Then I went to a doctor that specialized in preventative medicine. He did every test he knew to do and found absolutely nothing wrong. He finally called me (on a Saturday, which I thought was very kind) to tell me that he thought everything was due to added stress in the past few months. He talked to me about certain things I could do to gain weight and lower my stress levels:
The main thing that concerned him is that he found out that I ate standing up and never finished a meal without multiple interruptions. I rarely did anything for myself anymore. The doctor told me to eat while my small children were napping or playing with each other to minimize interruptions. He ordered me to slow down and enjoy my meal, sitting down the entire time whenever possible, and telling others they can wait as long as it wasn't an emergency.
He told me it wasn't a sin to set aside a small portion of each day to do something quiet that I really enjoy, something that relaxes me, especially right after eating. (Things like writing, reading, creating photo albums, crafts, sun and a magazine, or even sleep).
His next prescription was enjoyable kinds of exercise, which would rebuild and tone my muscles. Muscle weighs more than fat. Exercise would calm the mind and help put a smile on the face.
As for eating, he recommended against specialty diets... that most of them are more harmful than helpful. I was instructed to eat many well-rounded smaller meals throughout the day, drink lots of water, shop the outside of the aisles for fresh whole foods and try to avoid the processed foods found in the aisles of the grocery store, include the four food groups each day, avoid fatty/junk foods simply to gain weight, stay away from caffeine and excessive amounts of sugar, and take daily multi-vitamins to supplement and avoid insufficiencies.
Finally, he encouraged me not to lose myself in my daily responsibilities. So, what if the towels don't get folded today or the dishes don't get washed right away? I had to do them eventually, but I had to stop worrying and being anxious about details and keep the bigger picture in mind! He made it very clear that I am just as important as my family is. If I did not care for myself, I would be no good for anyone.