Post nasal drip - allergy or reflux?

[Loppylugs]

I had a moderate cold and cough about three to four weeks ago. Perhaps because I took Contac for several days, my sinuses became very blocked and for a couple of days I had really bad headaches and sinus pain. After the cold had more or less had cleared up I was suddenly plagued by excessive phlegm in my throat. It feels like the stuff is coming from the back of my nose and dripping down the back of my throat. I can breathe fine but feel congested at the back of my nose. It doesn't run or itch. I clear my throat (or try not to and sip water) all the time. This doesn't wake me up at night and, apart from a very slightly 'tight' chest (which is better for not coughing all the time) I'm fine. I seem to remember going through exactly the same thing last autumn and wondered if it was an allergy to moulds or something? The only other possible 'allergy' symptoms I get is intense itching in my ears sometimes, blocked eustachian tubes sometimes and slightly gritty eyes but nothing like I see other people with hay fever suffering. So I wondered, is this an allergy, leftovers of the cold or could it be reflux? I have no other symptoms - this state has been present for about two weeks now. Thanks.