Hello guys! I would just like to ask for HELP.

You see my current weight is 41.5 kg, and yeah, my weight used to be 44kg way back 3 months ago. I looked at myself in the mirror, and yeah, still a flat tummy. Can somebody give me advise on how to gain weight? I mean, since I am on hiatus, I am on an eat-all-day-sleep-for-10hours routine. And yeah, I eat rice and treat it as a snack. For real, I mean from breakfast to dinner to midnight snacks, I would eat rice, and I am also drinking vitamins. I really wanna gain weight and have a waistline greater than 25inches -_____-  please help me!

My friend suggested that I drink milk, but I am a bit allergic to it for no apparent reason, and I am not allowed to eat chocolates coz my migraine will kill me. so any suggestions? Please help! What food to eat :D I want to gain weight before I reach my 20s :)) Thank you! :)