longing, yearning - prolonged unfulfilled desire or need

disgruntlement - a feeling of sulky discontent

dysphoria - abnormal depression and discontent

dissatisfaction - the feeling of being displeased and discontent; "he was never slow to express his dissatisfaction with the service he received"

dissatisfy - fail to satisfy

unhappy - experiencing or marked by or causing sadness or sorrow or discontent; "unhappy over her departure"; "unhappy with her raise"; "after the argument they lapsed into an unhappy silence"; "had an unhappy time at school"; "the unhappy (or sad) news"; "he looks so sad"

displeased - not pleased; experiencing or manifesting displeasure