I was told by my Dr. that my Vit D was low – so I have been taking 2000 iu of (Nature Made) Vit D3 for a little more than 3 months. I just had blood work and my Vit D level did not change at all. My Dr. does not have any suggestions. Although I suspect that he doesn't believe I really took the Vit D faithfully – which I did because I was hoping to get an improvement of my energy level. Do you know what could be the problem?