Ignore the other guys.
Are you around kids? Do you have toddlers at home? Do you take public transportation? Do you work at a school or church? Do you work in a busy office?
If the answer to these questions is "no," and you're catching colds out of nowhere all the damn time, then you could have a serious illness that needs medical attention. It sounds like an inflammation disorder, which means that it could be anything -- autoimmune, a mold allergy, cancer, liver dysfunction, whatever. Get yourself checked out.
If you're around kids or work around lots of other people, what you're describing is pretty normal. When my kids were 1-4 years old they were sick every other month, and the whole house usually caught it. Sucks, but you get used to it eventually.