1. Hormones
a. Estrogen - causes a cessation of ovulation. The body actually INCREASES the conversion of calories into fat, in order to increase (replace) diminishing levels of estrogen in the body.
b. Progesterone - doesn't actually cause weight gain but water RETENTION and/or BLOATING.
c. Testosterone- diminished testosterone levels leads to LOSS OF MUSCLE MASS and LOWER METABOLISM.
Here's more information about Testosterone and Estrogen
2. Toxins
From Appendix B, How to Reduce the Estrogens in Your Environment, From Belly Fat to Belly Flat: How Your Hormones Are Adding Inches to Your Waist and Subtracting Years from Your Life -- the Medically Proven Way to Reset Your Metabolism and Reshape Your Body
Because some plastics shed xenohormones when heated, assume that they all do, and protect yourself accordingly. Don't drink hot beverages from plastic cups and don't drink water from a plastic bottle that has been left in the sun or in a hot car.
Don't microwave your food or drinks in plastic containers; avoid using plastic wrap to cover food in the microwave.
Get a good - quality water filter for your home. Drink and cook with filtered water.
...eat only organic, hormone free meat and dairy products and produce which has not been sprayed with pesticides.
Avoid...
aliphatic hydrocarbons (n-hexane)
halogenated hydrocarbons (carbon tetrachloride, trichlorethlene)
alchohols (methanol, ethanol)
cyclic hdrocharbons (cychlorhexane)
esters (ethyl acetate)
ethers (ethyl ether)
nitrohydrocarbons (ethyl nitrate)
ketones (acetone, methylethylketone)
glycols (ethylene glycol)
aromatic hydrocarbons (benzene)
aldehydes (acetaldehyde)
...don't use fabric softeners
...check cosmetics for toxic ingredients (throw them out) and look for organic cosmetics and even natural hair dyes.
Here are some good resources & products...
Natural Skin Care Make-Up
Burt's Bees
3. Food allergies
I suspect that I may have an egg allergy. It is the only food that I eat regularly, sometimes several times in a day and that the histamine in eggs may be causing or triggering an inflammatory response in my body.
Eggs are one of my favorite foods and provide a great source of protein so I hope the aforementioned is incorrect.
4. Heredity