what is the sickness if you are pale and weak

Only a physician can make a diagnosis and other information would be necessary before that can be done.
Anemia is a condition in which the body does not have enough healthy red blood cells. Red blood cells provide oxygen to body tissues. Iron deficiency anemia is a common type of anemia. It is due to insufficient iron.
Iron deficiency anemia symptoms may include: extreme fatigue, pale skin and weakness.
It isn't something to self-diagnose or treat. See your doctor for a diagnosis.

Maryann