What Additional Blood Work Should I Undergo To Help Diagnose My Anemia, Given My Low Ferritin And Hemoglobin Levels?

I am anemic It was discovered in 2015 and has been treated by a hematologist/oncologist before for almost 2 years without even being pinpointed as to diagnosis and now a new hematologist/oncologist has begun ferritin 2.7 hemoglobin 5.5 any other blood work needed I am glad to provide for a clue as to what I have?