There are many reasons why people seek help from a psychologist. I list a few here but this is not exhaustive and it may be that you cannot identify your problem just feel unhappy or ill at ease:
Depression
Anxiety
Obsessive Compulsive Disorder
Eating Disorders
Drug or Alcohol Dependency
Relationship Problems
Phobias
Learning Difficulties
Childhood Behavioural Problems
Memory Problems
Difficulties of Ageing
Adjustment Disorders
Trauma and Post Traumatic Stress