Why can't I gain weight?

[Leng]

I'm eating everything!  6 meals a day, plus snacks!  How do I can weight?  Please help.

[something]

You should forget what people say...U are who u are...do not worry what other think to much, moreover, u can try sports to help u to look healthy.Maby u are skinny but try sports and u will look and feel healthy...weight is not the biggest issue though...

[Leng]

I'm 19 and I'm 68 inches and my bmi is 16.4.  When my weight was 93 I decided to gain weight because people were being mean to me.  I also have autism and neurocardiogenic syncope and anxiety I think, and my doctor doesn't know why I am so skinny.  The only medicine I take is called Midodrine.  I eat healthy food and junk food.  I eat more than lots of people I know, and only sometimes my sickness makes me throw up.

[something]

It depends how old are you, have You always been thin? Do You work a lot(physical job)? Do you experience stress? Do You eat healthy food?