When it comes to gaining or losing weight, the bottom line is - calories count!
Weight management is all about balance (or in the case of someone that is focused on gaining weight..imbalance). The number of calories that you consume must exceed the number of calories your body uses or "burns off." For purposes of establishing a baseline, I would recommend that you record the number of calories you consume, per day, for a week. Generally speaking, you will need to increase this base by 500 - 1000 calories per day (depending on your weight gain goals).
If you need to tip the balance scale in the direction of gaining weight, keep in mind that it takes approximately 3,500 calories above your calorie needs to gain a pound of body weight. In other words, to gain about 1 to 2 pounds per week, you'll need to increase your caloric intake, above what you need, by 500-1000 calories per day (3,500 - 7000 calories per week).
Most of us cannot consume the amount of food required to gain the amount of weight we want. Select a calorie shake that has the amount of calories you need. If you want to gain a lot of weight get a shake with a lot of calories (ie - don't mess around witha 500 calorie shake if you want to gain 5 pounds a week...get the 2500 calorie version).
Eat six times a day plus snack: A major key to achieving growth is maximizing the amount of time your body is in a growth state. There are several factors that facilitate achieving this state; one of the key factors is having sufficient calories and nutrients available to your body.
During periods of normal activity, your body burns calories at a constant rate. In order to achieve consistent weight gain, your caloric intake must exceed your body's normal consumption rate. In order to exceed your body's normal consumption you must regularly have a greater supply of calories available to you body than it demands.
Adopting an eating schedule where you eat more frequently allows you to better
match your bodies calorie consumption levels that eating large meals infrequently and if you eat more frequently the variety of foods that you consume will also likely expand which will result in a better balanced diet.
In addition to eating six times a day, you need to snack in between meals. Snacking will help fill the voids and keep you from "going negative" (going negative refers to the periods of time where your body's calorie consumption exceeds the amount of calories available...in this state, your body begins to break down existing material (ie - muscle and fat) to produce energy; essentially your body begins to consume itself and weight loss begins.
Eat and take calorie shake near bed time:
Timing is everything. You want to eat regularly because your body is constantly burning calories. But, it is also important to take advantage of those times when your body slows down and burns calories at a lower rate. Consuming calories 30-60 minutes before you lay down will allow you to get the most value from those calories. Also, when you are resting, your muscles are growing..giving them more calories and protein during that period maximizes your growth.
Drink more water: Muscle is 70% water, increasing your water consumption is a key enabler for muscle growth and recovery. Additionally, you are substantially increasing the amount of food / calories that you consume and that your body must process. Your body needs more water to effectively process and support this level of consumption. General daily recommendations are 91 ounces for women and 125 ounces for men.
Aside from the above, you need to institute a weight lifting routine that incorporates heavy weights with compound movements and get sufficient rest.
Best of luck to you. Remain dedicated & consistent, fight through the tough times and meet your daily calorie requirements...and you will achieve the results you are seeking.