What Causes Fatigue And Loss Of Concentration?

Hi my name is Kenneth Cross, and I'm from Boston mass. I've been feeling very fatigued and have a lack of concentration. I feel like my thoughts are foggy all the time and I'm not functioning like my normal self. I have a hard time waking up in the mornings and look like absolute mess every morning. My old doctor said it is because my iron is low, so i started to take 65mg of iron a day and it felt like it helped for the longest time. I'm very healthy, i work out 4 times a day and I'm always hydrated. Some other symptoms i have, I'm not sure if they are relative or not, are feeling dizzy when i stand up, occasional diarrhea and difficulty socializing.