Question: How do I tell the difference between a head cold and a sinus infection?
Answer: Head colds are typically caused by viruses.
They last a few days; they're self-limiting. The drainage from the nose from a head cold is generally clear mucus. If that head cold persists longer than a week or 10 days, you begin to develop some facial pressure or headaches and the clear mucus drainage becomes discolored -- that is, yellow or greenish.
Then you think about perhaps that cold has developed into a secondary bacterial infection leading to sinusitis.