Whenever I have been off from running for more than a week (gasp-I know its hard to imagine a break that long) my first couple runs back are painfully itchy. It is unbearable and usually ends the run before a mile. Onset usually around .5 mile. I went for another test jog on the foot today and sure enough my thighs, butt and waist were so itchy I had to stop. Honestly almost draw blood scrathing trying to get some relief. I know scratching is not good, but the pain is unbearable at that point.

Any ideas of what is going on? It goes away after about three runs and only happens on the run even if I have kept up the bike and swim.