For years studies have shown that if you want more muscle you have to eat protein.
Generally Healthy adults is 1.2g of protein per kg of body mass. The question remains "How much more protein is required for change?" The answer is more than you'd think.
The latest studies have shown that it requires 60% more protein than the status quo to get optimal results. That is a lot of protein. Here some calculations for you....
If Sara Weighs 135 pounds that's 61.2 KG. Her body would require her to eat 74.64g of protein just for basic health needs. If she started exercising and wanted to compete she would have to increase that roughly 60% which would bring it up to 119. These are actually my requirements to maintain the size I do. So for all you females out there saying "i don't want to get big" trust me you never will. The amount of effort it takes for me to come close to that would shock you.
See Log below.

Breakfast-1 cup Egg whites, Spinach, mushroom- 29 grams of protein
Snack-Arbonne meal replacement shake- 20 g of protein
Lunch- 4 ounces of chicken breast with kale salad (costco) 28g protein
Snack- Arbonne Meal replacement-20g protein
Dinner Sirloin steak 4oz, Yam, Peppers-24 g protein
Snack- kirkland bar- 21g protein
total protein 125g

Now let say Ryan is 180 pounds that's 81.6 KG. His body would require him to eat 97.92 just for his basic health needs. If he starts exercising he need to increase that number by 60% that brings him to 157g of protein. So, for all you guys out there wondering why you're not gaining mass or those of you who want to there is a specific science to muscle mass. You have to log your food to know exactly what you are consuming and how to adjust..
If you use the same meal for Ryan but double the meat at lunch and dinner you would reach 169g of protein.

So ask yourself what does your diary look like?? If you are not logging your food you won't know what you are doing right or wrong in order to reach your goals.