Low haemogoblin level but normal ferritin level ?

Patient: I am a 21-year-old female. I had blood tests done a few days ago because I have not been eligible to donate blood several times in a row due to low haemogoblin. I would like to know what causes me to have a low haemogoblin level when my ferritin level is normal.RBC 4.15(3.85-5.02)Hb 10(11.2-14.1)HCT 32%(34-45)MCV 77.9(82.1-96)MCH 24.1(21.4-32.1)MCHC 30.9(32.1-34.3)Ferritin 5.7(4.6-204)