Dear Maha,
I guess the headaches and the leg pains are due to low levels of Hb, as you know the bone marrow expands when the HB drops and therefore it put pressure on the bones of the skull and other bones of the body.
In order to confirm this assumption, monitor these headaches after transfusion when his HB is high, if they diasappear, it means they are related to aneimia and i think you should then transfuse him at a higher level than he is used to, do not let his HB drop too much.
Please keep updating
manal