Is it feasible to change doctor? I don't know your height, but 40kg is low on anyone, and rapid weight loss is cause for concern no matter what you weigh. How tall are you, by the way? If you're experiencing nausea, they may be able to give you anti-nausea medication that works.
I'm one of the ones who got unwanted weight gain rather than weight loss, but I've had some experience with loss of appetite. Bland foods can work: rice, pasta, toast, potatoes. I generally do well with sweetish foods with a high water content: strawberries, cherries, and then feeding off carrot sticks, sugar snaps/snow peas and cherry tomatoes dipped in houmous. Getting started by nibbling something small, or the smell of cooking food, can help increase hunger - in theory; obviously something's wrong with the hunger mechanism for you, but it's worth trying. Spices and herbs may help, especially things like ginger.
Paradoxically, it may help to get hold of some dieting software so that you can learn more about nutrition. There are lots of foods out there which are relatively calorie-dense, and you'll only get on with some of them, so it'd be good to use this as a way of keeping a food diary and experimenting with what you can tolerate and how you react to things. Also record your weight, and make sure it's one of the types of software where you could print out a weight graph and/or food diary. The weight graph will be for convincing your doctor that it's a genuine problem, and the food diary will be useful if you get to a dietician, and probably also if you get to a gastro-enterologist.
As for meal replacement drinks, they're notorious for being vile. However, there are a lot of them out there, so it can be worth doggedly trying a whole lot of different ones to see if any work for you. I'm vegan, so almost all meal replacement drinks and the bulk of protein powders are no use for me. I have soy protein isolate, which tastes horrid, but I can cope with a tablespoon of it hidden into porridge if I add a chopped date to mask the flavour, or put into fake coffee made up with soya milk. There are various means of sneaking the stuff in.
If you're too tired to get out of bed and to the kitchen, keep non-perishable snacks by the bed so that you can just grab them.