First and foremost - get yourself a college ruled notebook. Track down every single morsel of food you put in your mouth. The number one mistake people make is "assuming" how much they are eating. People say they eat big, but in reality when you add it all up it's not that much.
Take 1 week and gauge your metabolism. By this I mean check your weight at the beginning of the week when you first wake up and then eat X number of calories each day (e.g. 2500 calories each day). At the end of the week check your weight again in the morning right when you get up. See if your weight went down, up, or remained constant. In your case, I would guess 2500 would be right around your maintantence level. If you dont gain any weight, try upping the calories to 3000 or 3500, and possibly even 4000, although 4000 calories is quite a bit.
Of course, remember, you MUST lift weights intensely during this time frame or else all this extra "bulk" you are adding will just accumulate as fat. Eat a good amount of protein daily (chicken, fish, beef, protein powder, eggs), good carbohydrates (oatmeal, brown rice, sweet potato) and healthy fats (natural peanut butter, olive oil, nuts, fish oil).
Hope this helps