When you have a cold, your Eustachian tube (a small tube that connects the middle ear to the back of the throat) can become blocked due to:

That plugged, underwater sensation in your ears is one of the most frustrating symptoms of the common cold. You might try swallowing, yawning, or tugging at your ear, but the pressure remains. This write-up explains exactly why it happens and how to safely clear it.

Most clogged ears from a cold resolve as the congestion improves. These methods help speed that along.