Same exact problem. It has always been hard for me to gain weight. My solution has been to eat as much solid food as I can at each meal and then top it off with an 800 calorie protein/carb shake. Another shake at night gets me through most the night. In case it is not enough and I wake up hungry I have RTDs by the bed. With this approach I was able to gain 10 pounds in 8 weeks. This also allows me to work out and build/KEEP muscle mass like never before.
Also consider your stress factor. On weekends when the work pressure subsides and I am more rested, and less rushed, I have more appetite and can put away a plate of food without it being a chore.