Why do I always get sick/a runny/congested nose after ALLOT of cardio?

[chris_aka_big_red]

Recently I've been doing allot of cardio exercises, and it has come to my attention that every time i decide to do a lot of cardio in one particular day, or for several days, i always seem to get sick and have a runny and congested nose. No other symptoms of being sick except an extremely runny nose where the fluid is clear most of the time, no color in it.

Any idea why this is?