Hi surely, I really do understand where you are coming from- andhow exhausted you must feel too!!! I am exclusively breastfeeding DS3 (5 months) and don't eat that much, and mostly eat 'healthy food'. I run most days and chase around after 3 boys under 5. I got batteries in the scales last weekend and at 5 foot 7 I weigh just over 7 1/2 stone , didn't realise I had become so thin! I definitely feel the worse for it. You must be careful not to get into a viscious circle of not eating then feeling shattered and then depressed and so not eating...
As for baby, my baby is really chubby, bright, healthy and active!!! It's me that is a bit tired. I think your body tends to naturally hang on to a little bit of fat, even during 'starvation'- natures way of protecting baby.
Some things that have helped me are
-exercising, makes you hungry and makes you think about using food for fuel
-eating little and often, eating what you fancy
-keeping well hydrated, loads of water and fennel tea
-make time for yourself, pleeeeeease look after yourself.
-I take the sanatogen pronatal plus omega 3 supplement
I echo what others say, baby will be fine, she will get everything from you, it's you that may suffer.