getting sick everytime

i've never been an avid fan of exercise...only because every time i start a routine i end up getting sick! why is this happening? i wash my hands after i work out to make sure i'm not eating any germs from the gym. usually i'll take a shower right after to rinse away sweat and grime. but every time i start to run (which is what i want to do eventually - marathons) or i start strength training i end up getting sore throats, and am out for the next week and a half. i will start my workouts moderately too.

anyone have any thoughts?

thanks!!