Normal ferritin but low hemoglobin

My ferritin was recently over 50, which is extremely good for me, because I had low ferritin for years. I'm only surprised that my hemoglobin is still low- 11.8 ( 12.0-15.7) In the winter it was already over 12 when my ferritin was about 30, so I don't understand why those results. My doc didn't say nothing to me.
What do you think? It was one week after my period. But also during the last year I never had hemoglobin over 12.5, although the ferritin was already in the norm range.