Hello, I didn't want to leave your message unanswered. It is really disheartening when they don't eat. However, they almost all do start eating again.
I got very fed up with people saying that about my DC, but eating has been going quite well since about 2yo. Some foods that were favourites at weaning are completely rejected now, e.g. philadelphia, yoghurt, etc.
My DC enjoys tasty vitamins e.g. Boots Multivitamin liquid is orange flavour and their Omega 3 is strawberry or orange. These are fairly cheap and often on 3 for 2, so not too expensive to try.
If your DS is given some of your meal, and you don't cook separately, then you won't feel your efforts are wasted to the same degree. I certainly feel that way and I think my DC is a bit better about it and tries to eat from our plates.
Try to make mealtimes fun and relaxed - easier said than done, I know!!! If you just have a conversation at the table while you eat but without watching what your DS is eating, you may find some food begins to be eaten.
Telling my DC that his meal is a favourite with one of his little friends worked, we've introduced ham, tuna, and boiled eggs doing this. I just say "I made this for you because it's name's favourite" and don't say anything else about it.
Some kids think spoons are the devil's work after weaning, and reject food on principle if it's offered on a spoon - my DN is like this, but will eat with hands.
Kids sometimes like foods you expect them to reject. My DC wouldn't touch sauages until chorizo was offered. Now all types of sausage are gobbled down.
Sorry for the essay, hope you get on better.