The EXACT same thing has been happening to me for several months now. It is so gross. The mucus is really, really thick and completely blocks anything from going down and eventually I have to go throw it up. I have also developed really awful acid reflux which I think is just from not being able to consistently keep get enough solid food down.
I used to be able to eat relatively normally, and occasionally something would get stuck. I would have piercing pain in the band area, the salivating, and eventually need to throw up whatever is stuck. This does not happen anymore, now it's this bizarre mucus thing. It seems like it happens when something has trouble going down. The mucus builds up behind it and I get a sensation of pressure building. It will reach a point where the urge to vomit becomes involuntary and usually after vomiting, I will feel something dislodge and go down.
I agree that staying hydrated really, really helps, I will have to try the mucinex, I'd not thought of that.
It is very frustrating however, because I find that I am not eating for long periods of time because I just don't want to deal with it. I end up starving and waiting until I have a little window where things are going down easy and then binging a little. Like I am trying to "stock up".