You are not alone in hating to get sick! Infections like the cold or the flu are major sources of stress for most of us and, unfortunately, they are very common, especially now as we move into the winter months.
For most healthy people, getting a few simple infections, like a cold, a few times a year is not a sign of an underlying medical problem and does not mean that there is something wrong with your immune system. Conversely, unfortunately, this also means that there is not much you can do to 'boost' your immune system.
Of course, what you can do is take care when you are in situations where you might be exposed to germs, such as public buildings and transportation. In particularly, frequent handwashing is a great way to cut down on the chance of getting an illness
This advice does not apply to you if you have a serious medical problem, like HIV or cancer - in this case, you will need to take special precautions to prevent infections and you may need special medications or vaccinations, something you can talk to your primary doctor
Also, if you just want general advice about how to stay healthy during the winter months, that is also something that a primary care doctor
would be happy to talk to you about at greater length.