It probably is part of ETD.
Sadly, many of the tests for ETD don't actually work very effectively. Audiograms and tympanometry are the 2 most likely tests an eNT will conduct, but these only really work properly with total blockage and/or effusion. If you have neither, they will tell you everything is normal, even if it isn't. It only takes a minor problem to interfere with it.
A test you can do that most ENTs don't employ is the Toynbee manoeuvre. It is safer than the Vasalva and actually tells you more about the state of the tubes. Effectively, you pinch your nose and swallow. If everything is working normally, you should feel the air drawn out of the ears by the vacuum created. If you then release your nose and swallow again, you should feel everything normalise. It may take 2 or 3 swallows of each, but this is still normal. If it doesn't, you have a problem with ETD.
I have had chronic ETD for over a year now and the standard tests come back normal, even though the Toynbee does not work in my right ear at all. I have also flown 4 times since it started and equalising my ears was almost impossible the first 2 times and excruciatingly painful on descent and the other times, I could hear this continual bubbling and popping from my right ear during both the ascent and descent. It is slowly getting better and I mean really slowly, so you have to be very patient with all of it. Apparently it isn't that uncommon for it to take 6+ months to fully recover from ETD and that depends on the cause...
Time is your friend and at 14, you have lots of it.