My main piece of advice is keep pushing your doctors to find out what it is, as sometimes they need a bit of prompting. A few of us here have had some bad luck with doctors, it really pays to be persistent. You always have the right to seek a second opinion if you need one.
I'm not a medical professional. I can give you ideas to look into, but I can't diagnose you with anything.
That said, if you do a lot of singing, speaking or shouting, might you have strained your voice or something similar? I've done it a couple of times, and it felt a bit like that.
As a general rule there are lots of conditions that can cause the same symptoms.
Have you looked up what conditions otolaryngologists (yeah... I had to look that up.. they're ear, nose and throat specialists) treat? Most throat related issues will be treated by them, so you'll be able to get a good list of possibilities to look into.
That issue sounds frustrating. It can be really nerve-wracking not knowing the reason for your symptoms. It helps if you have a reassuring doctor and can keep the level of risk in perspective. For example, the chance of having a serious disease is probably very low. I find that it can be very easy to confuse absolute risk and relative risk, which can make people think that the chance of having serious health issues seem larger than it actually is. Maybe you can ask your doctor to explain more about this.
I had a similar procedure last year for a different issue. There were a few days of a stomach upset/discomfort afterwards and bit of dizziness from the sedation but that was it. Luckily, mine came back all clear. It's important to remember that not finding a cause for your symptoms can often be a good thing as the doctor is able to rule out more serious issues. Before I had my procedure, my specialist said that she didn't think I had a disease but would perform the procedure just to rule it out given that I had a family history of it. She also spoke to me when I was in the recovery room to tell me that it all looked good.