seriously underweight

[abraama7]

i am 15 years old and the one of the smallest in my whole school, i only weigh 40 KG and ive tried so much to put weight on but i just cant. help needed and appreciated

[evewisewoman]

I would go and see your family doctor if you are concerned with your weight.
Perhaps your doctor could give you a referral to a dietician or a nutritionist.

[Caryopteris]

Being thin may be normal for you, but you could have a malabsorption syndrome like Celiac disease.  A doctor could check for you.  

I was underweight in school.  I remember I weighed 44 lb in 4th grade, 50 something in 5th grade, 60 something in 6th grade, and 80 something in 8th grade.  That translate to the range you are talking about.  I am 5'6", so I'm not short, either.  And I turned out to have Celiac disease, but not detected until much later.  

You can try having a liquid snack such as a green smoothie to see if that helps.  Try chewing your food better.  Eat more hamburger than steak.  Do any foods cause migraines?  You could have food allergies.