How to gain weight?

I am a nineteen year old who looks like a fifteen year old. With my height of 154 cm, I should weigh at the least 50kg but sadly I am just 40kg. Yeah I am skinny. Bones of my neck have protruded out and my eyes have diminished way into their sockets. 

I look as if I have been starving for almost a month. People can’t help astonishing when I say I am a degree student. Sometimes I try explaining, my body frame is such that, that I don’t gain weight fast. I show my hands too.” See they are small. I take smaller handfuls than all of you”. And then I point at my mouth.” See it is small. My mouthful is smaller than others”. But whatever I do people can’t help sympathizing. And with the arrival of dark circles, the intensity of OMG has risen.

Maintaining present weight is the biggest hurdle now.Which college student is able to grab something to have every morning? Especially when she comes from a hostel which is 4Km away from college. For a 9.00am class I barely manage to upright my body by 7.45am. 

I hate to go to restaurants. I hate trying out dishes at my place.I just have to keep myself alive. And I regret that habit.