You have to increase your daily food consumption. No amount of working out will help you put weight on if you aren't intaking enough carbs to actually turn into muscle mass. Double your eating and work out a lot, do heavy weights and do them as many times as you can. Also, to actually gain, you have to always increase how much you do every day. try adding 1 more rep every day, or every other day, and once you get to 10 more reps than what you started increase the amount of weight. If you always do the same workout every day you will quickly stop gaining. Try eating high protein foods, and fatty foods, but not sugary unhealthy stuff. Eat healthy, and eat a lot, drink lots of water, work out a lot, and eventually you will start noticing gains.