If your latest affliction hits you while you are in or just after you've been in the water, then you should try vinegar. If it is a bug bite, take an anti-histamine (liquid benadryl works best) and apply cortisone cream, both available at any pharmacy and probably places like Super Buy. Aloe is good for lots of things and the advice about local remedies is always good too.
Once you are out of the water, keep everything dry. If you are doing a bunch of biking and hiking and swimming, you'll be wanting to keep your netherparts as dry as possible. Don't forget to keep something on your feet, no matter how tempting it is to walk barefoot in the sand.
Always treat a cut immediately.
Learn to keep your distance from things growing on the reef and wear a skin for accidental brushes. But frankly, if you don't have enough control to keep from touching the reef, stay the heck away from the reef. Everytime you touch it, you are killing something that has taken years to grow.
And don't forget . . have fun out there, lol.