The Eustachian Tube connects the middle ear to the back of the nose (see Diagrams — Upper Respiratory Tract and Anatomy of the Ear). If this gets congested from a cold or allergies, pressure can build up in the middle ear. It’s like what happens during airplane take-offs and landings, and can hurt to varying degrees.
We can sometimes diagnose this by examining the ear with an otoscope (the instrument hanging on exam room walls), & noticing that the ear drum looks “retracted.” Lots of clinicians fail to appreciate the subtlety. However, Eustachian Tube Dysfunction is so common, that if a patient has ear pain and no other cause seems apparent, I treat with Allergy Medication. Patients tend to get better, so maybe I’m right (or maybe placebo worked, or maybe they would have gotten better anyway). I don’t give decongestants, because I don’t know of any proof that they work. And I never recommend common nasal sprays or drops like Afrin®, Neo-Synephrine®, etc; they work fine, but after 3-4 days the nose is so accustomed that it can be impossible to stop them (see Rhinitis Medicamentosa).
If you have ear pain, & your provider says “everything’s normal,” ask “Is the TM retracted?” [“TM” is common medical jargon: abbreviation for “tympanic membrane,” i.e. ear drum]. A “retracted TM” looks pulled back, almost horizontal, because of negative pressure behind it. Ear discomfort PLUS a retracted TM almost always signifies Eustachian Tube Dysfunction.