Hi masim
I used to be in the place you're at and it's down-right frustrating. However, there are several things you can do to increase your mass. Firstly, can I assume you're of African/Carribean ethnicity?
What has my ethnicity got to do with this? You may ask. Well, quite a lot actually.
Knowing your weight, height, and your ethno type gives us an indication of what your frame and make-up is like. Many guys who are thin and tall and of African descent, are genetically and metabolically different from a European thin guy. Mo Farah, is for example, an amazing athlete and is thin but very muscular. Now a white European guy of the same frame and height, and also a distance runner will probably have slightly more body fat and less muscle mass, except for the calves and lower legs. Knowing your descendancy can help focus on the areas that need work, while maximising the potential of areas that need less.
You say you eat three meals a day. I assume these are spaced out around five hours apart?
Before you can look and play around with the components of your diet, you need to understand your calorie requirement and how much each macronutrient (protein, carbohydrate, and fats) contributes calorie-wise. The easiest way of doing this is using a rounding up system called
Atwater Factors:
1 gramme of protein = 4 kcalories (or commonly called calories)
1 gramme of carbohydrates = 4 kcalories
1 gramme of fat or oil = 9 kcalories
*1 gramme of alcohol = 7kcals
*
Alcohol is nutritionally empty and should never be considered as part of a diet.
Energy Balance and Incremental Weight Gain
You are probably eating in the region of 2300kcals to 2800kcals per day. If what you are consuming daily now is keeping your weight level you can conclude this to be your maintenance level, or energy balance. Now you need to increase this intake by around 500kcals a day to start. This can be achieved by eating another main meal during the day or supplementing your diet with a high calorie carbohydrate/protein shake. These have between 400kcals to 900kcals per serving and usually can be increased with adding milk. All things being equal, you should see a gain of around 0.75 to 1.5Ibs of weight increase per week. If you do not see any progress within two weeks at this level you may want to increase your intake by another 250 to 500kcals.
So now you've increased your calorie intake what else can you do?
Well, if you're not a keen athlete and weight gain means to more to you than running everyday, you really need to consider what you want more. I'd strongly suggest that reducing your running frequency to three times a week, and cutting each run down to a mile or two, will spare many calories and lend to weight gain. Don't forget, running or jogging (or any cardiovascular activity) feeds on muscle, carbohydrate, and fat stores, and these fuel stores need to be constantly at their maximum, and untapped, to elicit mixed weight gain.
What foods do I need to eat?
Well, for general weight gain (muscle and fat mass) you don't need to focus on the quality of food a champion bodybuilder or competitive athlete will need to observe. I'd advise keeping your diet generally as it is (presuming a normal, balanced diet?). However, I would focus on getting plenty of complex carbohydrates and all sources of natural protein. For example:
Complex Carbohydrates
Breakfast cereals
Oats or oatmeal
Rice (preferably brown)
Potatoes
Yams
Pasta (preferably brown)
Wholewheat or brown bread (white will do).
Protein
Chicken breast or thighs
Turkey
Beef
Pork (dependant on religious observances)
Lamb
Mackeral
Tuna
Cod
Haddock
Sardines
Eggs
Milk (semi or full fat)
You can mix many variations of the carbohydrates with proteins and stick some salad stuffs and/or veggies with it for nutritional balance. To add taste, add your favourite sauces or condiments but try to use salt sparingly.
Basically, the trick is to eat more and do less. If you want mor elaboration you're welcome to PM me.
Best of luck
Craig