There are lots of reasons why people lose weight at different weights:
Gender: Men typically need 2500 calories a day to maintain their weight, women 2000. So on 800 a day a man is deficient by 1700 calories, while a woman just 1300 calories – a man should lose weight more quickly.
Exercise: Over the last 2 days I’ve done runs that burn 600 calories each. That means that, on balance, I’ve effectively only had 200 calories per day.
Lifestyle: Someone that has an active job – they’re up and about, moving around all day – will burn more calories each day naturally. They’ll lose weight more quickly as a result
Muscle mass: Someone who has strong muscles will lose weight more quickly because they burn more calories each day. I weight train. That’s useful for me when losing weight.
Weight: The heavier you are, the more quickly you lose weight because you need more calories you use each day.
So, I don’t know if any of the above apply to you. Some you can work on yourself, exercising for instance and being active, others you just have to accept.
And perhaps it’s also just the way your body reacts to the change – everyone is different.
Keep going and good luck.