Why does my left ear get plugged upon getting up?

Need more info. You may be sleeping on that side and getting congested in the back of your throat by either post nasal drip or reflux esophagitis (acid). This creates transient obstruction of the eustacian tube (which drains the middle ear into the throat) and a feeling of being plugged up. There are several other possible explanations but you would have to go see an ENT doctor. Good luck.