There is some evidence that being stress and fatigued and not getting enough sleep may have some settle effects on your immune system. This is not the same thing, however, as saying you should necessarily sleep more. Each person is different with respect to the amount of sleep that they require. If you are getting 5-6 hours of sleep per night and feeling well rested, then that is probably all of the sleep that you need. On the other hand, if you feel fatigued all of the time getting 5 hours per night, then you may need to increase the amount of sleep a bit.
There are other things you can do to help boost your immune system, including eating nutritious, balanced meals high in fresh fruits and vegetables, which contain antioxidants. Exercise can also help, as can avoiding tobacco and alcohol.
You may also want to talk to your primary care doctor
about getting a flu shot
. These are recommended for most people, and they can reduce your risk of getting the flu and, in particular, of getting a bad case of flu. The flu shot should be available now in your primary care doctor's office.