I'm a contra alto, and i'm going to guess that your cold is just taking so long to go away because of stress. i had a cold show week of my first lead role back in november, but i drank like 8 bottles of water a day. and it worked.
so i'm just going to suggest cough drops and lots and lots of water. =]
Two roads diverged in a wood, and I?
I took the one less traveled by,
And that has made all the difference.