I started out at 118lbs and 6'1". Yeah, real skinny for a guy. Then I hit the weights and started gaining till I hit about 135. Still skinny and I couldn't get anywhere.
Then I discovered the magic of the squat. And that gave a jolt to my body to put on the weight. I ballooned up to 165 in months with an amazing increase in appetite. The first night I did squats I was so hungry I ate 2.5 servings at dinner time where normally I would just eat my regular portion. Then I stopped because I don't like being too big. Plus I like doing body weight exercises which I do now.
Go to hardgainer.com to find out more about the magic of the squat.