I lost an awful lot of weight when my ds was born. I was b/f him and not eating well myself. It was a vicious circle, I was feeding in the night so I was tired, b/f also drained me of energy, this meant that I had no appetite, and even the thought of having to get up and make myself a sandwich was too much.
I went to the doc and she thought that I had thyroid problems too as my white blood cell count was low, she wanted to do a bone marrow test on me. That frightened me so I persuaded her to put it off for a week. During that week I ate All Bran, red meat, brown bread, I really tried and when she tested again my blood cell count was normal. However I was still skinny, I dropped down to 7 stone when normally I'm around 8.5, I'm tall too so it really doesn't look good. In the meantime ds was happily piling on the pounds and turning into a very big baby. I had to stop b/f, once I did this my appetite slowly returned.
The things you can do are to buy snack foods from the supermarket that require no effort to prepare. Scones, crumpets, soups, cereal bars, fruit compotes, mars bars, ready-made sandwiches, just to encourage you to eat. I would get put off if I had to make something myself. Drink lots of milk too as this is counted as a food source.
Don't exercise until you are eating better, otherwise you'll either faint or make yourself unwell.
Hope it gets better!