About 4 months ago I started getting fatigued...

At first I thought it was something physical (as opposed to mental, not saying mental problems don't have a physical basis). I considered thyroid problems, hormone problems, everything. I went to the doctor and they ran blood tests and even gave me an MRI. The only results are that I have practically zero iron and have extremely low levels of several vitamins. Their only solution was to prescribe me a multivitamin. Did my loss of appetite cause the vitamin deficiencies or vice versa? Who knows?