I am sorry you are going through this.
Because I have my own issues I always feel unqualified to give advice. That being said sometimes helping other people helps me so I hope you don't find me too hypocritical.
It seems to me that you are very much focused on your youth. It seems like so many of us hit this place where we don't know what we've got til it's gone and then ignore the not so pleasant parts of our past. And you did have unpleasant parts in your past that made you gain and lose weight many times, as you have admitted yourself.
It's important to remember that what we did in our youth effects or now and what we do now effects our future. You still have many wonderful years ahead. Why contaminate them with unnecessary mental leftovers from your youth?
I am in my late thirties and I can tell you that my youth was not pleasant despite the fact that I was not fat. I never had weight issues until my mother's death in my mid twenties. I never yo yo dieted either. But I can tell you that I do not want to fight getting older. I want my middle and elder years to be the most fun an active ever. I think you want that, too. But since you feel like you cannot attain that goal you are focusing too much on your past.
Your body is in a rage right now due to hormones. I would agree with a nutritionist consult. I also agree with a food journal if only to assess how you feel after eating certain foods. Some foods will make you "crash" some foods are to "heavy" some give you gas. But they all have alternatives! I like smoothies because they are easier to digest and packed with nutrients and can be very filling. This morning I had a fat free vanilla yogurt, frozen blueberry, baby spinach, skim milk and oats smoothie. Very filling and easy on my stomach. However it had the calories of a full meal so I had to watch my dinner.
About those hot flashes, haven't had those yet, but my sister-in-law (who is awe-some!) Tells me that she battled hot flashes and exercise with swimming and water arobics. She is lucky to live on a lake to make that easier, but she also took classes. The coolness of the water was easier on her joints and helped to keep the hot flashes at bay. Unless you enjoy intense gym workouts the main component, from my understanding is a symbiosis of diet and movement. I do Zumba on the Wii and Wii fit as well as walking. If I have eaten healthy the exercise begins to feel good.
I do hope you feel better soon! *hugs*