This is tough. The quickest way to pack in calories in small amounts of food is via nuts or fat. Could you make yourself some crackers from ground or chopped nuts, oats and butter, then eat a couple with a sliver of cheese or some cream cheese and maybe some tomato or cucumber to balance the flavour if it feels too rich.
For breakfast, full fat Greek yoghurt with a few berries and chopped walnuts.
Or low sugar granola with full fat milk.
Make your own bread (or get a loved one to make it for you) and add lots of seeds and ground nuts, melted butter or olive oil to it. A single slice, toasted with a bit of butter will be rich in calories and savoury.
Or scrambled eggs - much easier to eat 2-3 eggs scrambled than any other way as they seem smaller. Cook them with butter and a bit of single cream. Have on a slice of toast with butter. Even if you only manage a few mouthfuls, there will be sufficient calories in eggs cooked this way.
You can make thick soup from lentils and carrots and onions, then add a swirl of cream and some sprinkled toasted seeds on top (leave the seeds out if they'd make you gag.) Eat a small bowlful with a slice of bread and butter - garlic butter if it tastes less fatty to you.
Before you eat, sit a moment. Take four slow deep breaths in through the nose, out through the mouth. Gently tell yourself: this is to keep me well and strong. I will take my time, in peace, to eat it.
You probably won't put on weight but these might help you not lose more.