Hello! I contracted what seemed to be a routine cold about 6 days ago, but after a weekend of rest, hydration, and relaxation, I ve had a constant headache for the past three days, clear, but steady supply of phlegm (nothing that s running down the back of my throat), and a tight/sore neck. I have not had a fever at all. At what point do I start to think my cold may have turned into a sinus infection?