Health Help: someone related to medicine please!

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I need help soon! I want to know how many kcals/day should I ingest , because I think I'm eating less than what I should. It's easy, you may think, "eat more"; but I just can't. I tried to. But everytime I do, I gain a lot of weight. I'm 17 and 1.78 mts tall. I weigh 62.5 kg (just in case you need my info)