I'm a 25-year-old man without major systemic disease before. I am actually a medical student now. During the general examination this year, i noticed my Hb level around 12-13 g/dL. Follow up data in the following months showed 12.7 (04/2018) --> 12.8(05/2018) --> 12.4(06/2018) --> 12.6(07/2018). Normocytic(84), boderline hypochromic(31.5) with borderline Hct (38.5%) during the last examination. WBC, and PLT were both within normal limits and i also had normal differential count with no blast cell. Other lab data like total protein, albumin, ferritin and stool occult blood were all within normal limits. Due to these problems, i looked back for my past examination history and found an examination 7 years ago (when i was 18-year- old) showed also Hb level around 12.6 g/dL with similar other lab data. HbEP was also arranged for further survey and revealed Hb A 97.8%, and Hb A2 2.2%.

The reticulocyte count during the last examination showed 1.3%, which would be bone marrow hypo-proliferative if i corrected it with reticulocyte index. I wonder whether do i have to worried about some bone marrow problems and seek for bone marrow aspiration?
Or, is it just not suitable to use reticulocyte index to calculate reticulocyte when my Hb level was only a little bit below the normal limits? (RBC count = 0000/microL, absolute reticulocyte count was normal)

Can Hb 12-13 g/dL be a normal variant in a generally healthy young adult?
What other differential diagnosis do i have to keep in mind?