Extreme calorie restriction can be addictive, even if it was completely accidental. The way your body responds when you don't eat enough may just feel really good, and so you start to severely dislike the idea of being full or having food in your belly or using any extra energy to digest, which can result in something that feels like not being hungry. Just like people who consistently overeat have a hard time understanding the difference between being hungry and just wanting something to munch on, people who consistently undereat (even if accidentally, like yourself) can suddenly have a hard time telling the starvation-induced-high from the feeling of not actually needing food.
So, I agree with everyone else about eating more. I don't know enough about to say it should be carbs or something else, but since you've already gotten to this point, I'd definitely say eat more calorie-dense foods that go down easily, because eating when you feel like you don't want to (for whatever reason) can be unpleasant and can reinforce the cycle. So eat nut butter, cheese, etc. Eat all the things that people trying to lose weight can't eat because they're just so delicious and calorie dense that people can ingest 1k calories of the stuff before they know it and it doesn't make them feel full. Same with yams, not just for the carbs, but again because they go down easily and don't tend to leave you feeling stuffed the way, say, a steak will.
Just like people who overeat need to heal their brains and satiety/hunger signals, people who consistently undereat for whatever reason need to do the same (and a few months is certainly enough time for this to happen).
Let us know how it goes!