Myelofibrosis usually develops slowly. In its very early stages, many people don't experience signs or symptoms. As disruption of normal blood cell production increases, signs and symptoms may include: 
Feeling tired, weak or short of breath, usually because of anemia
Pain or fullness below your ribs on the left side, due to an enlarged spleen
Easy bruising
Easy bleeding
Excessive sweating during sleep (night sweats)
Fever
Bone pain
