This is one we don't get very often!
Probably your body just needs to get used to having 1200 cals. Don't force yourself to eat--that would be counterproductive--but do try to increase your calories overall so you reach 1200 average. If you aren't hungry for a snack mid-morning--don't have one! Instead see if you can add some nuts or foods like that (as modkittn said) to your lunch. Easy does it... no rush!
Jay