As someone who struggles to put on mass, it took me about two years of solid lifting and eating to get from 77kg to 81kg. The hardest thing for me was, and still is, eating enough. Personally, I found that 'gainer' drinks didn't do nearly as much for me as whole foods, and it was a lot easier on my wallet. If I was to suggest anything, I would suggest treating meals like workouts, but thats only because it's been working for me. Protein will make you feel fuller faster, so eat your carbs and fats first in the sitting is something that's been helping me get more food in.
If you're anything like me, long bouts of 'cardio' will make you drop weight like its nobody's business, so I found the best conditioning for myself was barbell complexes, weighted carries and sled pushes, or slow paced uphill walks.
Like handsome rob said, you might be overestimating how much you eat. I've been setting myself a 'minimum' ammount of calories per day and If I can eat over it, that's great, but I make myself reach 4000 cals of food/milk etc before I add in supplements.
Hope any of this helps