What is it called when someone always says they are sick and need to go to the doctors?

A person with HYPOCHONDRIA has a preoccupying fear of having a serious illness. This conviction persists despite appropriate medical evaluation and reassurance of good health. People with hypochondria are obsessed with bodily functions and interpret normal sensations (such as heart beats, sweating, and bowel movements) or minor abnormalities (such as a runny nose, a small sore, or slightly swollen lymph nodes) as symptoms of serious medical conditions. They may also focus on vague and ambiguous physical sensations, like "a sore liver" or "tired veins." One form of this disorder involves a preoccupation with a single organ (such as the lungs) or disease (for example, cancer). Negative results of diagnostic examinations do little to decrease a patient's anxiety about his or her health, and he or she continues to seek medical attention.