When you have a fullness in your ear feeling it's usually caused by blocked Eustachian tubes.
When we yawn our Eustachian tubes open up and when they don't or are blocked we get a fullness in our ear feeling.
Ear infections can also cause a full ear feeling.
To unblock your ears you can try yawning, chewing gum, sucking on some candy or inhale and then exhale gently while holding your nostrils closed and closing your mouth and keeping your mouth closed.