I have fluid built up in my right ear. i was told that i could take claritin, but i have benadryl (diphenhydramine) on hand. can i use benadryl (diphenhydramine) instead?

Yes: Yes if it's an allergy. Take it at night since it makes you drowsy.

Yes: If effective, you might find it wears off quickly (3-4 hours) and might be more sedating than Claritin. If this is eustachian tube dysfunction and you decide to pick up Claritin, I recommend a trial of nasal Afrin, but don't use it for more than 3 nights in a row (dependence develops). Let your doctor know what works.

Antihistamine : Both Clairitin and Benadryl (diphenhydramine) are antihistamines. They both decrease secretion of mucus they also decrease excessive response to allergens from the immune system.