Cough due to Nasal Polyp Draining Down Throat

Sounds stupid I know, but I had a nasal polyp removed 4 years ago and it has returned. The problem is I don't want surgery again and want to know how I can get rid naturally. At the moment I have a cough which is worse in a morning and I know it's my nose that drains onto my chest during the night. When I sniff up I can taste this awful snotty taste going down my throat and onto my chest, which then I cough up. Sometimes its green like snot which I've just swallowed.

Please tell me of a product I can buy over the counter and that I can get in Spain as that is where i live.

I have a big phobia about going to see doctors, please help.