I feel for you, I enjoy my food. Many years ago my wife was prescribed sachets of powder that were made up with water in to an orange drink to boost her appetite. We can't think what it was called but it worked.
If you are not eating enough you are going to feel fatigued and not be happy in yourself. I'm sure you know all this but as well as trying to eat the 'right' food, eat any high fat, high calorie food that you fancy in small quantities but often. Your stomach will get used to having food in it again and it might trigger hunger pangs and your appetite. Rice pudding, custard, ice cream....you get the idea.
An apple always makes me hungry, no idea why.
If you do like to take supplements, have you tried this?
Amazon.co.uk User Recommendation
Most supermarkets and places like Superdrug and Boots sell it, too.