I have to eat 1 small meal every three hours, Could you help me?

k i got Diagnosed two weeks back, I'm 13, and 5'7, and have a heart pace of 49 Beats per minute. I know. 49. So yesterday, me and my doctor decided to f**k anorexia. I'm now forcing myself to eat around 1800 Calories a day. But the thing is, My stomach is the size of a large apple and i have no clue what to eat. I got recommended to eat around 1 small meal every three hours, but i don't know what to eat, obviously something nutritious and healthy. What do you think? What should i eat every three hours? :) Thanks.