Reply To: Complaints of severe fatigue led my PCP to run a Vitamind D 25-Hydroxy blood test. My level came back at 17ng/mL. She prescribed Vitamin D2 at 50,000 IU once a week. I understand that D2 is not what my body needs to correct my defiency but do they prescribe D3 is that does or can I only get it OTC? And can I switch from D2 or D3 or should I discuss that with my Dr first?