4. Weight gain and obesity without eating more than before
In regeneration phase : strong swelling in regeneration phase A, the metabolism is slower, the excess energy and food doesn't get out of the body to keep a healthy balance, it stays in, gets stuck. From the body's point of view it is an increase in weight and size, but in function I think it is a reduced function. Circulation, metabolism, energy and nutrient exchange is slower. As it is obesity, it is an ongoing problem, probably swelling in stress phase and in regeneration phase as well. 
Brain layer connected: Cerebral Medulla
 
5. Underactive thyroid, weight gain and inner coldness, tiredness
reduced in function, not producing enough hormones. Inner coldness and tiredness reminds me of freeze response, dorsal vagal on the autonomic ladder. So it could be that that's a stress response and after that, in regeneration phase comes the strong swelling in both phase A and B.
I couldn't decide whether it is Cerebral Medulla or Cerebral Cortex. I think maybe if there was a weight gain and weight loss fluctuation, (no swelling in stress phase) then it would be Cerebral Cortex response. 
If it is a constant swelling then I vote for Cerebral Medulla. 

What other weight gain causes do you know?  Medication - steroids, imbalance in feeding and moving the body, underactive thyroid, hormonal changes and imbalance, eating food regularly that causes weight gain like sugar, unhealthy fats, too much carb. Needing protection, a protective layer. After losing touch - a need to get closer by growing bigger. Unconscious self-sabotage - to unconsciously prove a network of limiting beliefs, e.g. I can't do that, I can't ever get to my dreams, there is something wrong with me, I am too big, I am too small, Life is hard and I can't cope, I need more resources, as I haven't got enough, I need protection, I don't deserve. My real me need not to be seen. I am not enough, or I am too much.