What can I do for excessive mucus that runs down the back of my throat? It chokes me and I cough a lot.

Try an antihistamine. Mucus that runs down your throat can have many different causes, and you usually need to see a doctor to figure out the cause and allow for specific treatment. Chronic sinus infections, allergies or acid from the stomach can be common causes. Using an older antihistamine like chlropheniramine can help in some cases and wouldn't hurt to try.