I have been cycling and running for a few years and over the past two months have never felt worse? Am i under eating over training i just cant figure it out. I just went on vacation and took four days off. Today i went out for my morning run hoping to feel fresh but was met with a slow weak and painfull workout. After the first half mile my legs felt soar and my head pounded. Over the winter and springg months i had worked my running up to 8 miles a day and now a five mile trip is a challange. Please any help i could get would be greatly appriciated.