Each "cold-carrying" person has a different tolerance for Vitamin C. Some people will find that 250mg six times daily is perfect, while others will take as much as 1,000mg ten times daily. Perhaps the most important thing to know when using Vitamin C is that it is best taken in intervals.
Get rid of those tissues! Used tissues harbor bacteria and viruses. Cluttering up your counters, bathrooms, etc., with used tissues increases the chances that you and your family will be re-infected.