How can I stop this infernal coughing?

I have a head cold -- nothing more. I have just as much energy as usual, etc. However, I'm having so much sinus drainage that I'm coughing until I vomit. How can I lessen this? I have in my dorm some Sudafed PE ("guaifenesin and phenylephrine HCl caplets"). I'm in Mississippi, so I can't by anything with pseudophedrine without a prescription, so that's out. Help!