Estrogen does not automatically make one gain weight. It also doesn't automatically move fat away from one's belly.
Whether with or without HRT, diet is the secret. I don't mean dieting but rather eating a nutrient dense combination of foods that the human species evolved to eat. This makes your body work properly and will heal a multitude of ailments caused by eating food like substances rather than real food.
Start by eliminating:
All added sugar
All foods with added sugar
All processed food
All wheat products, i.e. bread
All processed oils (corn, canola, etc.)
Eat lots of vegetables, lots of good fats, a fair amount of protein, and some fruits. Eat slowly, until you are satisfied, and then stop eating.
As a bonus eat fermented foods with live cultures. These include sauerkraut, kimchi, yogurt, kefir, and kombucha.
Exercise will help but is not necessary for weight loss. It is necessary for good health though.
Conform and be dull. —James Frank Dobie, The Voice of the Coyote