Not getting appetite like before

It’s been well over 2 years since I’ve reduced my appetite. I should’ve like increases it because I’m still in developing phase. I eat only in the morning, and then in the evening. I usually have a milkshake to gain extra and easy to gain calories to gain weight as I’m below my expected weight limit. But milkshake’s are not gonna cut it, also I don’t do alot of exercise, just roaming in home, getting groceries outside and bedrotting. I even have a messed up sleep routine. I want to atleast gain 4 kg in 2 months this summer. Tell me how? Must consider that I feel full easily and when I leave my food due to being full, I never eat it again later. Drinking water after the food also makes me full. Force feeding myself results in a restless night of vertigo and nausea.