Most external ear infections are caused when the ear is exposed to "dirty" water, and isn't dried properly. The lack of drying is often due to a wax buildup in the external ear canal. So, just squirt a little Pledge in there once in a while to reduce that waxy buildup...
Seriously though, keeping the canal clean can be accomplished with occassional flush with Hydrogen Peroxide. Warm it to body temperature, and when you are in the shower, just pour a wee bit into your ear, making sure it goes right in by "squishing" around the entrance to your ear with your finger. If you have guck in there, you'll hear it fizzing and stuff. After a couple of minutes, rinse your ear out with clear water. Once every month or two is probably enough, and whatever you do, don't be jamming a Q-Tip in there... it just compacts everything.
Assuming you have an infection, use an ear drop such as Burosol or Domboro-otic. To speed things along, soak a bit of cotton batten with the stuff, and loosley pack it into your ear before bed... Odds are, you'll be spiffy in a jiffy!
Certainly, a trip to your Doc to get a look is a good idea, but the steps above won't hurt either... unless I suppose if you have perforated your eardrum, which (a) doesn't sound likely and (b) probably would have healed by now anyway...
A simple trick to test if you have an infection... tug your ear lobe.. if it makes your ear hurt, you probably do. If it doesn't increase the pain, you might have an internal infection or trauma.... both require professional help!
I agree with the others though, the use of a wetsuit hood probably doesn't matter with respect to an infection. Long term exposure to cold can cause hearing loss years later though, so be careful. If your hood isn't comfy, get one that is.. or a drysuit with a dryhood, such as a Viking.
BTW, I'm not a doctor. But after several years of lifeguarding, a few of competitive swimming, 20 years of SCUBA instruction, and 31 years of diving (including 2 summers commercially in Hamilton Harbour and Lake Erie way back when...) I have learned a thing or two about ear puss. Good luck!