Hi Minu, if you have lack of appetite along with weight loss then you could be in serious problem.Any illness can adversely affect a previously hearty appetite. If the disease is treatable, the appetite should return when the disease is cured.Loss of appetite can cause unintentional weight loss.The common Causes are emotional upset, nervousness, loneliness, boredom, tension, anxiety, bereavement, and depression, anorexia nervosa, acute and chronic infections, HIV, pregnancy (first trimester), cancer,hypothyroidism or due to few medicines like chemotherapeutic agents, amphetamines, sympathomimetics including ephedrine, antibiotics, cough and cold preparations, codeine, morphine, demerol or digitalis. Get yourself evaluated.