I know, its crappy, isn't it?
I shouldn't worry too much. I feel like I have eaten so little in the last few weeks, been sick so much, I have lost 12lb and am permanently exhausted. However, last thing before bed I make sure I take my Pregnacare tablet just to be sure I'm getting some sort of vitamins and minerals into me. Also, I've been quite lucky in a sense that when I do fancy things, they tend to weird combos but are nutritionally very good .i.e brocolli, almonds, cranberries and pears. Just a very tiny bit at a time, though.
You'll have time to make up for the lost appetite, but for now just ensure that you are properly hydrated. My midwife recommended isotonic drinks because I have been really thirsty too, they rehydrate you more effectively than water or juice alone so you can 'top up' with them.
If you're really worried, speak to your midwife to get some reassurance and advice.