One of my dog's ears all of a sudden just started bothering her. Please help asap.?

Hi, my mom just got back from walking our dog...about 15 minutes in she started acting like she was experiencing some discomfort in her ear. Shaking her head about constantly as if trying to dislodge something from her ear. She wasn't even able to get any of her business done outside b/c of this. This happened out of nowhere, she was not exhibiting any behaviour of discomfort until this point. My mom hypothesized that perhaps a bug flew in, even though she has very floppy ears but she had nothing else to go on. I examined the inside of both ears and they look fine. She's acting normal too, licking us and wagging her tail about. But she's still shaking her head, and we can tell her ear (we're not sure which one) is still bugging her. We know her ears are clean, we take her to the vet regularly and they always tell us how clean her ears are. Is it time for another vet visit? Or is it really nothing too serious? We're also thinking perhaps a bee stung her or something. Really don't know. Any tips or advice would be helpful though, thanks.