Just doing some surfing on weight gain and found this article. It's geared towards body builders but there are some great tips for gaining weight.
Here's a couple of the best tips:
"Stop doing so much cardio."
"Building muscle is rather simple. It requires:
Consistency - Not missing workouts. Consistency plays a major role in making quality gains.
Progressive Overload (that's using bigger weights and/or more repetitions of the exercise) - You must get a lot stronger than you are now. No exceptions. There is no "easier" way to build muscle.
Good Tools - Using the best possible exercises, when possible. The better your tools (exercises), the better your results.
Patience - Gains take years, not weeks. Look 2 years down the road, not 2 weeks. You can make amazing progress in 2 year's time, so dedicate yourself to sticking with a plan."
- from an article by Steve Shaw
Check it out and "good gaining"!
Nobody can make you feel inferior without your permission.