Vin - I was surprised that the suggested calorie intake was only 1800 per day. I was told that aggressive treatment puts tremendous strain on the body causing calorie burning to rise sharply. I weigh about 190 and it was suggested that my daily calories should be over 3000.
Even now, 27 months out of treatment I am still on nearly 2500 per day. Every person's metabolism is slightly different, but that 1800 number seemed really low to me. I am glad you getting good professional advice about that. Question that dietician again when you can and mention the much higher numbers given to many of us. The body can't heal without fuel.

Be really aggressive with your docs about the vomiting. There are a number of meds that can really help. If you two demand enough, they will help you find something that works. And chat with your dentist (and your docs) about Diflucan for the thrush. My vomit problem was always worse when I had thrush going on, though I don't know why. The mucous becomes less and less an issue, but the reflux irritation in the throat can cause the vomiting to be more likely.

Chat with your doc - you may be able to substantially increase the Robittusin dose every once in a while. Ask first. Double the water intake and cut the mucous problem by half (or so).

Get that humidifier running, push the fluids and calories and know that it WILL get better. Walk a bit several times per day - it helps build energy and thirst. Keep a daily chart of intake, exercise, meds, barfs and sleep. Set tiny goals, meet them and then set more. Get focused on meeting higher goals instead of just handling the misery of the next hour. Focus on what IS working, not on what isn't. Keep us informed. Fight hard, be strong. Tom