"You're not eating enough food" is the answer about 98% of the time.
I'm(M17) 176cm(5'9) and 48kg(105 lb), my BMI is 15.5 and I'm REALLY skinny, everytime somebody sees me they get either scared or concerned, and at the beginning i said i was fine but now I really feel like I need help. We contacted many different doctors in my city(I live in Italy) and nobody knows what my problem is.. we(my family and I) did many exams looking for problems with metabolism and we got nothing, we were thinking to get my self hospitalized (as you know, it's free in Italy xD) but they asked us a kind of "hint" of what medical department(like "cardiology" i don't know if it's correct in English) i should go in, and our doctor told us he'd inform himself but didn't tell us anything.So my questions are, what could be my problem, what department should I get hospitalized in and in general what should I do?Any answer is appreciated and I'll try to answer every question