You haven't really stated how much and what you eat. There are other factors as well, such as your somatotype, i.e., ectomorph, mesomorph or endomorph.
Also, there's your activity level. How often do you train, and how intense? Is your job a physical job where you burn a lot of calories throughout the day? Do you do a lot of cardio or involved in sports which requires a lot of calories to be burned, such as basketball?
It's a cliche, but if you want to get big, you have to EAT big! You need to consume more calories than you burn if you want to gain muscle.
I'm an endomorph, so I put weight on easily, so I have to be careful and not eat too many calories, especially simple carbs and empty calories.
My diet is as follows:
Breakfast 1: Protein shake, roughly 30 grams of protein in the AM.
Breakfast 2: Oatmeal and eight eggs (4 with yolk, 4 without yolk)
Lunch 1: Protein shake, roughly 30 grams of protein with an apple
Lunch 2: Eight ounces of chicken or 97% lean beef with high fibrous carbs
Pre-workout shake with 30 grams of protein and an apple or some fruit
Post workout shake with 30 grams of protein with a fast-acting fruit, banana
Dinner 1: Eight ounces of chicken or 97% lean beef with Brussel sprouts, green beans, Lima beans and mixed veggies
Dinner 2: A cup of low-fat cottage cheese
Night time: A casein shake, roughly 30 grams of protein.