There are two classifications of ear infections: acute and chronic. An ear infection is generally considered acute when it occurs with a sudden onset and normally resolves within a timely manner( around 3 weeks).
When a person experiences repeat infections, or an infection that does not go away, it is considered chronic.
Sometimes a person can have an earache without an ear infection. For example, this could be due to a cold that causes ear pressure/ discomfort. In other cases, a cold or other condition may cause an ear infection as a secondary infection.
Absolutely not. Some ear infections are viral. That said, antibiotics used for a viral condition would have no effect on treating the infection.