Who knows what's in Sambucol, it's not tested.
3 to 4 weeks is not just a cold, that's much too long. Go see your doctor! Viral infections such as colds don't typically last more than 7-10 days.
You may need to see you GP!
Otherwise and as posted on another thread, I suggest to use Sambucol which is made from black Elderberry. It woks wonders for me!