Is it normal that I have a weight cap and can not be NOT underweight?

I have tried eating a lot and have times where i overeat consistently. I cannot go past that highest weight which is still underweight according to BMI. and as soon as i stop eating or lessen my eating a lot or dont eat for a day or so... I literally start feeling the bones in my hands more and i start losing weight very easily. I know some people are thinking Give me that problem lol but i seriously haven't heard of this before... Losing weight so easily yet not being able to gain weight, the way i have it.
Is it normal that I have a weight cap and can not be NOT underweight?
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