What is it with all the Colds!

I'm loosing count now, can't remember if this is number five or six since Christmas. This one though has come with a nasty twist ... a hacking cough!. Woke up on Sunday with an 'odd' kind of throat and thought that this must be a hazard of being a pro singer but then when the coughing, aching and breathlessness started I decided this couldn't be 'singers flu'. Since then it has been downhill and I feel awful now. Needless to say, no running has been performed since Saturday and I can't see much being done for a little while yet. Was only thinking today that I have never been so unhealthy as I have since I took up running. I was expecting to be glowing with health and buzzing from the frequent endorphin rush but I don't seem to have experienced either. Just how much running do you have to do?