It's a matter of trainign yourself. You've been eating so little for so long your body and mind are used to not feeling hunger. You also feel full after very little amounts. It's the same as those with anoreixa who are hospitilized and put on meal plans. The reason they need to be supervised is bescause (aside fromt he health issues), they have trained themselves to ignore their body singals, and thus refeeding themselves will be dificult because you feel like youre going against what your body is telling you.

At this point, you cannot rely on your body or mind to tell you what and when you should eat. Your breakfast is not ridiculously huge, making up for a skipping lunch, so you shouldn't be planning to skip lunch (skipping meals isn't good anyways..you can slow down your metabolism further). If you have an aversion to eating big meals, eat lots of little snacks. Either way, up your intake to about 2000 Cals- starting first with 1800, then workign up again. You will feel full and will not want to eat, but you have to. It will be easier and will pass with time, so stick it out if you want to be healthy.