Unless you are kissing someone romantically, you aren't going to get their oral herpes. It won't swim thru water to infect you either.
At your age, about 1/3 of your friends have oral herpes. It's incredibly common. By the time you hit your parent's age twice that many folks have it. By the time you hit the retirement village, it's closer to 80% of adults have hsv1 orally. Not many of us get thru life without it. http://www.ashastd.org/herpes/herpes_learn_oralherpes.cfm is a link for more reading on cold sores to check out.
You've been out in the sun and the water. Odds are what you are worried about is just chapped lips and normal things going on on your tongue. Listerine is very drying so perhaps stop using mouthwash for a week too and see how that goes. You also could be having something called angular chelitis on the corners of your mouth or it could just be a zit like you think it is. If it dosen't clear up in a week of using just a regular ole lip moisturizing product ( vaseline at bedtime is helpful too ), ask to go see your doctor for a better work up. It's not likely this is oral herpes going on. Don't pick at things and don't open your mouth so wide that you cause the skin to crack again too until it's healed.