Your BMI (admittedly a poor indicator) would put you at only just out of range. At that weight your body would be adapting metabolism to prevent further weight loss. It will continue to adapt to increased exercise and reduced calorie intake in order to maintain enough ‘fuel in the tank’ for times of when food isn’t available.
If no sugars (particularly fructose) are in your diet then it will have no option but to metabolize fat as a glucose source. I’d try strict keto or carnivore.