Afrin to the rescue ... again

I just got over yet another cold. Do I have no immune system whatsoever? Why do I keep getting sick? Here are my theories:

1) allergic to something in our new house (but what? and what to do about it?)

2) a result of stress from work (I've been putting in a lot of overtime since my promotion - although I have my own office now which is pretty sweet :))

3) I haven't exercised in ... oh ... a year or two. Ok, ok, I walk and bike-ride in the summers and do occasional "abs of steel" workouts throughout the year ... But I haven't been to an actual gym since California. I hear sloth's not so good for your health.

4) I'm kind of a kid when it comes to fruits and veggies - I just don't love 'em, and I'd much rather snack on carbs, ice cream, and baked goods :) I did just buy some multi-vitamins though, so I'll be testing the "you need to get your vitamins" theory shortly.

5) greater exposure to kids once a week at Elmbrook's jr. high group. This theory was suggested to me, but I think it's a weak one. I don't feel I get close enough to any of them long enough to really extract their germs.

If anyone has any other theories, the knowledge of which could result in fewer future sicknesses, I'd be happy to lend an ear.