I Have Thick Mucous In My Throat. I Cough And

I have thick mucous in my throat. I cough and gag trying to expel it. Most of the time I am successful at expelling it, but sometimes it can also be difficult to spit out. It feels like a mucous plug and sometimes when I swallow it I can feel a lot of it draining. I cough a lot because of it and usually when I cough there is a pain in my chest and a sore spot in my throat. What do you think might be causing it? I know you cannot give a direct diagnosis but based off of what I am describing what do you think it is?