Low calorie intake will not cause necessarily cause weight gain, but it can cause your body to go into "starvation mode", in which it will hold on to fat stores, thinking there's not enough food coming in.
If you are 206 pounds, you definitely need more than 1400 calories...
I'd be real interested in knowing your current thyroid levels - that would be TSH, Free T3 and Free T4. If those levels, especially Free T3, which controls metabolism, are not right for your body, you will not be able to lose weight.......
Have you ever had adrenal testing done? Excess cortisol can cause weight gain. What about insulin resistance? That, too, can cause weight gain/inability to lose........
If you have current blood work for any of these things, please post the results, along with reference ranges, which vary from lab to lab........
I definitely think your calories intake is too low, but that would not cause weight gain, I don't think.
I really wish doctors would take the time to listen to their patients. They tell us all that can go wrong if allow ourselves to get obese, but they won't listen when we feel helpless to stop weight gain!
Stress is definitely a problem, too. It can also cause weight gain. Do you have any way of lessening the stress in your life?
You might also consider finding another doctor.
Sometimes when your body is under extream stress it may decide to store everything and not give way to losing it even through exercise. I know gaining ton of weight can be stressful but try to relaxe. Do something to relaxe more, like if you enjoy reading, read more often or listen to music. I gain waight really fast under stress. Even through diet and exercise it slows down my weight losse. Maybe if you just slightly up you calorie intake it may allow your body to less feel like it needs to hold on.