Do Low Ferritin Levels Damage The Body?

Hi. I've had anemia for the past 2 years and have been on iron supplementation (3 per day for several months, 1 per day for the past 9 months). My blood levels are all normal now, except for the ferritin which is 77. I find my brain tires easily and I just can't think straight. Also, I'm not sure if I should be taking more than 1 iron tablet a day now. Is a low ferritin level a problem? Do I need to get it higher, and if so what do I need to do?
Thanks for your help!
Louise