What Causes Popping Feeling In Ear While Sneezing/yawning?

for last 3 days i have a popping feeling in my left ear; but it almost sounds like a rubberband or the sound you hear when you are under water. I went to my GP. She said ears are clear, no wax, no infection... it happens when I sneeze, yawn, hiccup, etc... its quite annoying. I've been sleeping on that side hoping to drain it (if that was the issue). Any idea of what this could be??? never really had ear issues before.