When I had lived in the US I was astonished by the number of people that seemed to have constant cold and/or cough. Little later I had observed that the majority of the sick people did the following:
1. never stayed in bed with fever, or when they needed rest
2. wore inappropriate clothing for the weather (flip flops in freezing weather, wet hair and no hat, shorts for running in sub 35 degree weather, etc.)
3. drank ice cold beverages while sick
4. constantly took stupid medicines that only masked the symptoms but never tried to cure the root OF THE PROBLEM (like trying to get rif of phleghm by using common sense approach - blow your nose for god sake, it's not embarrasing).
5. Never washed their hands after touching dirty objects (keyboards, door knobs, class desks...)
When I had pointed this problem to my constantly sick teammate, I got ridiculed by him and by my coach as well. Guess who never had problems to get rid of some stupid cold?
If you feel weak, even without fever, go to bed and stay there for couple days, the body obviously needs the rest. Masking the ilness with pseudoephedrine-like medicines won't cure you.