How to treat constant cold problem with phlegm passing down the throat?

Hi doctor,

I am 29 years old. I am having constant cold problems, not a runny nose but I always can feel phlegm passing down in the back of the throat throughout the year. When certain conditions like prolonged exposure to cold temperatures, symptoms like dry cough, heaviness all over the face especially in cheeks, eyebrows, sneezing, congestion in nasal passages, snoring, etc, happen. After following remedies like steam inhaling, and drinking warm water situations usually comes back to normal but the feeling of phlegm passing down in the back of the throat remains all the time. Is there any permanent solution to this? Or any effective ways to deal with it?

I am not using any medication regarding this, otherwise using Thyronorm 25 mcg for a thyroid issue. Please help.

Thank you doctor,

There is no throat pain. No long term nose block. As mentioned, when exposed to cold temperatures, I get nose congestion for one or two days and get relieved. But this feeling of mucus or phlegm passing down the throat is constant irrespective of severe cold. I am attaching the throat pictures.