How to increase weight? Nothing works why?

Hi All,

I am trying from quite a long time to increase my weight but guess what never been able to increase weight. My current is around 130 lbs and my height around 5 feet 9 inches
Tried gym, tried eating more times in a day, trying eating junk food, cheese, milk etc. nothing works upon me.
Please suggest?
And by the way wanted to mention 1 more point. I am a vegetarian.
How to increase weight? Nothing works why?
Post Opinion