When I quit smoking, MANY MOONS AGO, it seemed like EVERY illness going around hit me hard for the first month or two, but after that I felt great! A friend of mine told me that when you take away something that your body is addicted to, your metabolism/immune system kinda goes into shock. If you stick it out, you'll feel much better soon.
My dad has COPD (chronic obstructive pulminary disease) from smoking, and I GUARANTEE if you met him, you'd never wanna smoke again.