WoW, it seems like quite many people having the underweight problem here. Oh well, me also "Very thin", only 55 kg with 175 cm height (Yup, totally a walking skeleton for sure lol) Eat 6 times per day, but my weight is remaining the same, sigh... 

I used to be one of those guys who said "I eat a lot but I never seem to gain weight" Then, I read about proper ways of gaining weight.

Even though the portion of your meal is big, eating 2 or 3 meals a day isn't going to help you pack on pounds.

People who tell you to eat fried chicken or roti canai before bed clearly don't know the proper way of gaining weight. Yes that can definitely help you put on weight, bad weight which is fat.

Its not that difficult to gain weight. Eat 6 meals a day. I workout in the morning so my pre-workout meal is my breakfast.

My diet was like this :

Morning/Pre workout : 5 eggs, 2 wholegrain bread, 1 tblspoon peanut butter
Snack/Post workout : 500 ml milk, 100 g almond
Lunch : Steamed chicken breast or pasta, 1 tblspoon olive oil, 500 ml milk
Snack : 500 ml milk
Dinner : Grilled chicken breast with green peas
Before bed : 500 ml milk

I stuck to a simple workout program called Stronglifts 5x5 and you only have to train 3 times a week, 45 minutes a day.

I was consistent in eating 6 meals a day, never skipped my workout and got enough sleep and rest. I gained 10 kg in 3 months, from 54kg to 64.

Just be a little more disciplined and consistent when it comes to gaining weight and spend a little more on food. Take the effort in reading, understanding and searching for information.