What Causes A Feeling Of Mucus Stuck In The Esophagus?

I feel like there is vomit stuck in my esophagus, but I do not feel nausea in my stomach. It's been happening for a few months, but it was very rare and now it happens more often and lasts longer. Sometimes eating or drinking carbonated drinks helps. It has felt this way all day today - by far the longest it has occured. I have never vomitted from this.