Will leukemia cause low hemoglobin levels? how quickly does it progress if acute?

Why do you ask?: If you have been discovered to have an anemia, and you are concerned it is leukemia, do not wait another day -- ask your physician whether abnormal cells were seen on your smear and/or white counts &/or platelets were abnormal. If not, it has another cause. Anemia may be very sudden or insidious depending on the type of leukemia. But i'm concerned first for you.

Unlikely: Unlikely acute leukemia, plz see a hematologist. Anemia has many causes at your age most common being iron deficiency. Acute leukemia without therapy is a fatal disease.