What causes ear pressure and no pain in a 28-year-old?

Hello doctor,

I am a 28-year-old male suffering from weird left ear pressure for six months, I am a healthy airline pilot. My symptoms are mild ear pressure only in the left ear. No pain and hearing are fine. Sometimes I feel discomfort (not pain) in my left side neck and left throat as well. I went to the ENT who checked my ears and said it is normal and asked me to do a pressure test (because I am a pilot) which came normal. The neck ultrasound is normal. He ruled out any ear infection and said it might be TMJ. I looked out TMJ symptoms on the internet and found it is not applicable to me because in TMJ issues pain will be present (especially when closing or opening the jaw). Honestly, I do not feel any pain around my jaw. I do feel a cracking sound in the left jaw (yes around my left ear) while opening and closing, but no pain. The pressure I feel comes very quickly either when I rest the back of my head, on the chair, or when I lying back of my head on the bed. Also, this discomfort is very noticeable when I close my eyes. Sometimes the valsava maneuver makes me feel better for a few seconds. I was diagnosed with viral thyroiditis last year and it became normal (without taking any medication) a few months ago (follow-up tests reports were within normal ranges). I was diagnosed with GERD as well. What could be causing the problem in the ears? Please help.