You might want to consider going to the doctor to get it checked out. I'm prone to ear infections when I swim. A few years ago I had one so bad I couldn't sleep or do anything. The regular antibiotics didn't work so I had Cipro drops. That's powerful stuff but it cleared it up in two days.

If you think it's swimmers ear (you do triathlons, right?) you might want to consider before- and after-swim drops to prevent infections in the future. You can mix alcohol and water, or you can buy prepared swim ear drops.