Hi, I am a runner and lately I have felt an odd fluctuation in my energy levels. Sometime I feel extremely weak, (This occurs most of the time) where I basically become fatigued and out of breath,my strength also seems to lessen. The rest of the time I feel just okay, where I am to perform at a decent level. Before this running season I felt great, my energy level was always high (Except for low iron, which I fixed since I take iron all the time). What could be the problem?