A dreary mood due to someone's not phoning you when you'd expected or wanted him/her to.
In a classic "Miss Piggy's Advice" column in Muppet Magazine, a mid-teenage lad complains about how his main squeeze always suffers a major bout of melancallie whenever he isn't able to "give her a jingle" in the evening, despite his repeatedly having explained to her that he's a farmer boy and thus has chores that often prevent him from being free to simply sit and "yack on the horn" for half an hour. He finishes his message to said "sage sow" by indignantly asking her, "So what am I supposed to do?!" Being a selfish brat herself --- AND a fierce feminist --- said pink-skinned flat-nosed advisor unhelpfully snorts back, "You're supposed o call her." Some help SHE turned out to be there! :P
A less-than-cheerful mood due to abdominal pain, either because you're suffering it yourself or you're having to expend significant time and effort caring for someone else who's going through it.
Many parents become melancolic when their offspring have long crying-bouts for no apparent reason.