Really tiny wrists underweigth

I am 16 years old and I burn calories really fast, no matter what I eat I don't gain weight. my weight is 53kg and my high is 178cm. I am so tiny around the wrist. Any ideas of how I can gain weight? I have tried the last week not to train but didn't help, so I though maybe if I trained more and gained more muscles?
Really tiny wrists underweigth
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