** so... should I eat more? **

Hi
Basically I was anorexic as a young teenager and have yo-yo'd around with my weight ever since, I've never been overweight but I've been a bit more curvy than I'd like (BMI about 22), and I've been intermittently VERY thin. Usually getting thin again after I've gained a bit is pretty easy for me, I have not really got a problem with restricted eating, but recently I've found that my body no longer responds to limited food. I put on about half a stone over last summer and I've been trying to get rid of it ever since! I don't want to be too thin (I don't have an eating disorder any more), I just want to lose about 4 kilos (which would leave me at a BMI of 18.6, which is healthy).
I have been eating about 600kcal a day for a good few months now, and I exercise pretty much every other day. I am not miss-calculating my calories, I have a lot of calorie counting experience from my ED days when I used to follow strict meal plans during recovery. I know that sounds like nothing caloriewise but for me it feels like plenty of food and I don't get hungry much, its because of my past and all the times when I would go an awful long time with no food at all. Please don't judge me for eating not too much - also I am short (5ft 2) and am quite a small build.

So basically my question is - has anyone else increased their calories from a low amount in order to get their metabolism in gear, did it work for you? How long did it take? I've decided that I don't want to go on like this, I'm not losing any weight, and if I go out for a meal or have some cake for a birthday or something I always gain, which is so depressing. I really want to get my metabolism back in gear but I don't want to gain weight!! I still really want to lose these 4 kilos! Any suggestions or success stories from people who have had similar experiences?
Thanks so much!