im 25, 188 m aand was about 67 kg. Had same problem couldnt rly gain any weight. Now im 80-82 kg and all I can say is...you have to eat A LOT. I was eating between 3000 and 3500 calories per day. It is quite hard but you need a good diet and also training. Basically, this is something I used to eat. Cant recall everything tho.
Breakfast:
5 boiled eggs - usually 2 whole eggs and 3 just the protein (the white stuff
)
macaroni with white cheese. It is very common here in Bulgaria
or instead of the macaroni you can try oatmeal with yogurt or milk.
Before lunch I was eating 1 pack of rice cakes and a protein shake.
Lunch:
2 chicken fillets about 400 grams usually on grill + boiled rice or mashed/oven potatoes but not fried. With some delicious garlic baguettes. I used to buy them from Tesco (UK) and they had huge amount of calories and carbs
Then again until dinner I was eating another pack of rice cakes, small portion of nuts (because of the fat), bananas, fruits and protein shake.
Dinner:
cant recall if it was 200 or 400 grams of salmon with rice or potatoes. You can try the sweet potatoes, they are quite nice.
So in the end I had about 3000-3500 calories, 75-90 grams of fat, 200-250 protein and 400-450 carbs. Numbers might differ since I dont remember very well how it was and my notes are not with me now
This was my main diet I made myself. However, with the time I've learned to look at what each food gives me and change it a bit. Like sometimes I could eat a pizza or something but still be in these boundaries.