Anemia?

Spec
6 weeks ago I was diagnosed with iron deficiency anemia and put 1 iron tablet per day. (100mg, plus my prenatals have 25mg). 
After doing that for 4 weeks I had a follow up and somehow my levels were even lower! My doc increased me to 3 tablets per day. I don't go in for blood work until next week, but I'm still feeling ordinary. 
Just wondering what others would do in the same situation. 
I'm wondering if they should have looked into why 125mg of iron per day didn't help?