At my dr appointment i had low ferritin but all other blood counts were normal, dr suggested an iron supplement. when should i have levels retested?

About six months: You may get ferritin level done again after completing iron replacement treatment.

I get this question: often. Low ferritin = "total body" iron deficiency, not necessarily anemia- YET. Why then give Iron if you do not have anemia? Answer - low ferritin is a PRE- ANEMIC state- Simply, because you may become anemic in the near future if you remain deficient for an extended period of time.