Our 2 year-old daughter just had tubes put in for the second time on Monday. Her almost-4 year-old brother has had 1 ear infection. She has had 10 or 11 (5 this year after tubes in February, 2009).
She never displays symptoms. The only way we know is that she begins to drain badly from her nose. And, there are usually 2 ears infected. She never has fevers, she never complains about her ears hurting or tugs on them. She's just really susceptible to them, and I've learned that 2 rounds of tubes is more common than I would have thought.
Generally, the infection is caused by the improper drainage of fluid that than becomes infected with bacteria that the ear would normally battle on its own.
Since babies that age can't communicate well, I'd recommend calling the pediatrician and asking what they think based upon the symptoms. They'll let you know if they want you to bring her into the office. I always think it's better to call and let them determine if you need to come in personally.
Good luck. It could also be allergy related as bad as the pollen has been, but her symptoms are vague, and I'm not medically trained.