Go onto bodybuilding.com they have all the information about everything that anyone could ever want to know, countless articles, eating plans and training programs for hard gainers. And I can guarantee you that although you think you're eating a lot, your not at all.
Until you count how many calories you actually eat, you wont realise how little you eat. Theres a good chance you're a little disillusioned, I always thought I ate loads and would always say how I eat loads I just cant put on weight.. Checked how many calories i was eating and it was around 2000.. 500 less then recommended, and if you wan't to gain weight you probably want to hit 3000 at least, maybe a few hundred more.
I found the easiest way to hit that is protein shakes with blue top milk, whacks on the extra calories and gives you protein post workout, that way if I eat 2500+ calories in good food, I can aim to make up the difference with a decent sized protein shake post workout
You really have to up your calorie intake. As a hardgainer myself, I had to up mine to 4.5-5k before I started putting on weight, which was tough (though I do a lot of cardio, which partly explains the need for the higher than usual amount).
You need to eat more, once you've eaten and are satisfied, half an hour later eat another meal, after each meal drink as much milk as you can. Eat untill way after you're full. I started a lifting program in december, 2 weeks later I was only 0.3kg heavier, i was confused, the program guranteed colossal gains, i then read that it said you're not eating enough, so i ate more, and i mean LOTS. 1.5x my old portions, more meals, more milk... Two weeks later i had gained 2kg.