Blister in back of throat!

So I've suddenly developed a severely painful sore throat, like above and beyond what I have ever had. I have a wealth of health issues but this doesn't seem to be related in the slightest.

I also suddenly developed what looks to be a blister in the back of my throat, on the wall behind the uvula. I know this was not there last week because I went to the ENT (twice!) and had a camera down my throat both times. My throat pain did not start until well after this, so I'm sure it's not irritation. I have also suffered from those deep ulcers in my mouth since I was about 2 years old (I'm 20, female, FYI) and it is nothing like those. In addition, I also have green, thick, sticky phlegm coming from my chest, definitely not my nasal area, I can feel the difference.

So I'm kind of freaking out for multiple reasons and I would like to have any input on what this could possibly be.

I also have coughed up a few tonsoliths a few times this past year but nothing too serious or frequent.

So ANY feedback would be wonderful since I'm at a complete loss. And this is definitely similar looking to a blister you'd see on your foot (that looks to be filled with water or fluid.)