Why is it taking forever for my cold to go away?

Usually when I have a cold, it lasts for 4-5 days max, but this has been lasting for 3 weeks. I can't taste food which sucks, I can't breathe through my nose, I have a terrible cough, and all the above. I've been taking NyQuil, cough medicine, and Sudafed every day and night and nothing is helping. Why is it so pestering?