Edit: Bringing sugar back into my diet is not an option because I feel like shit when I taste anything with white sugar added. Feeling severely dehydrated and no matter how much water I drink it doesn't get better for half a day after taking sugar. Also it doesn't taste good anymore. Eating more is also hard because of underlying medical issue (when too full I get all sort of medical issues).
From what you say I think this part is the reason why you are losing weight tbh. As Umbra stated in the earliest replies; when you spend more energy than you put in your mouth you lose weight.
People I know lose weight as easy as they gain weight in that age gap. Eating too much sugar products are not natural for humans anyway. I wouldn't worry if I were you. Still, go see a doctor again if you are so concerned.
My father used to be around 100kgs himself, after he had blood related issues he cut down sugar to 0 and now he is 70-75kgs iirc.
A few days ago I was in the bus, a slightly overweight woman approached, asked if it passes by the courthouse. Driver saidthat she needed to walk around 5 minutes after getting off. She then refused to use the bus. Maybe if she accepted that and many similar things in her life, she would be in a better shape. Or yesterday when a friend of mine insisted on using the elevator to get to the lecture class. But what do I know, it might be more challenging for people who aren't skinny af as I am. The only thing I know is only wealthy people with servants used to be overweight before the age of technology.