There are no cures for a cold. And Vitamin C after the fact doesn't help. It's too late at that point (but still always a good idea).
However, to help dissolve the symptoms a bit, if it's a head cold, make a tea out of Blue Vervain.
If it's a chest/bronchial cold, make a catnip tea.
If it's both, you can use both without issue.
I usually add some mint leaves to the tea as well as a bit of raw ginger.
To help with a sore throat, the teas will help temporarily, the ginger will help lengthen the relief a bit, but if you can get some actual licorice root (not the candy, but the actual root), it has a numbing effect if you chew on it a bit.