I have suffered from severe bronchitis and coughs that do not go away since I was a child. What helped me the most was seeing a Chinese herbalist who made up a tea for me to drink for 3 days and gave me some Chinese supplements to take. The tea was totally awful, but really worked.
Also the garlic as you mentioned has helped too. I take the enteric-coated kind (Enymatic Therapy makes a really good one called Garlinase which doesn't make you smell) and just take it constantly every hour or so. I also have taken this with high doses of Ester-C.
The other thing you can do if you are comfortable with it, is to do a fast, preferably water, if not, juice and give your lungs and your body a chance to deal with the inflammation and also to clear things out.