My Homoglobin Has Dropped From 16.4 Mg To 11.3 Mg

My homoglobin has dropped from 16.4 mg to 11.3 mg overhe last nine months. There is no occult blood, I am an insulin, Lantus, dependent diabetic. I recently experienced post herpatic neuropathy for about six months in the area of my right oblique muscles. I have been to an Internest and vascular surgeon in the last month. What could be the cause for my anemia?