I lost 31 kgs in about 10 months and now I currently weigh 57 kgs.
age -23
height - 158 cm
waist - 29"
Should I continue losing weight ? or should I stop and maintain weight/build muscle?
I still have belly pouch left.
My goal after losing weight is to get six pack abs.
But I am stuck in a problem.
Everyone keeps telling me I look like a sick person, I have sunken cheeks and I look very weird and ugly !!!
I don't know what to do at this point.
Please advise me whether I should continue losing weight/ maintain ? eat in surplus to build muscle ?

Everyone's build is different, and there's no way for anyone to advise you what your perfect body is like over the internet, unfortunately (and it would be dangerous to do so anyway). I can say that you're about my height (5'1"/5'2") and about 125 pounds, which is well within a healthy weight for your height with wiggle room both up and down. Unless you're really ripped with super low body fat or have a very large build, it seems odd that you'd look sick and have sunken cheeks at that weight, but of course I can't actually see you. I think talking to a doc/nutritionist/trainer would be a great idea at this point. It's possible too that after losing so much weight so quickly you may have some extra skin, which may be factoring into that residual belly pooch.

Perhaps a better question is, what do you want to look like, and is that a realistic goal? And then once you decide that for yourself, talk to some health professionals about what that looks like for you.

It's hard to say if you should lose more weight without knowing what you look like. You don't necessarily have to choose between losing more weight or building muscle (you can lose fat and gain muscle at the same time).

Are you getting enough sleep, eating a healthy diet, drinking enough water, and eating enough vegetables? If not, doing those things will help you to look (and to be) healthier.

If you want six pack abs, the most important thing to do is eat healthy (avoid sweets, refined carbs, and deep fried foods), because you need a good diet if you want your body fat to be low. You also need to do weightlifting if you want a six pack. Focus mainly on compound exercises (e.g. squat, deadlift, bench press, pullups).