On zpack & prednisone for sinus infection i've had since jan. snot now red-tinged like liquid from fresh tomato. was yellow. why color change? bad?

Specific diagnosis: 6 months of an alleged sinus problem is way to long to suffer from this. You need a more specific diagnosis. You need a CAT scan of the paranasal sinuses to determine if, indeed, you have a sinus problem. That is first. Second, Z-pack is not an appropriate antibiotic for upper respiratory bacterial infection. Prednisone is appropriate for a short period of time.