Pica Pica. Too late to do anything now, right when you get it spraying with anything containing ammonia helps (windex, pee (have a friend help or you may hurt yourself), etc.).
There's been plenty of debate over what Pica Pica is but Green Reef reported it as being an algae bloom that happens to occur around the same time the thimble jellyfish appear. Others say they are actually caused by the offspring of the thimble jellyfish which appear in the millions around April or so.
Use Eurax loton. Antihistimine if you need it.
A vinegar solution is good to neutralize the stinging cells. Just apply to sensitive areas immediately after getting out of the water, then apply a good antihistamine cream to the area to stop the itching. Bring some Diprosone Cream with you or pick some up at a local pharmacy, it's the most effective relief for the itch from pica pica!!! Or use Eurox lotion on your skin and if it's a bigger problem, use Eurox and buy Atarax antihistimines. Available over the counter.
To prevent use Safe Sea (safesea.net, or Safe Sea is available at dive shops), you can buy it on the interent, not sure if you can get it on the island. We brought it last year in April, used it the first two days, but didn't run into any. Did meet one lady that had it where her wet suit ended around her neck. Seems the affected areas are where they get trapped by clothing. Check with your guides as well, some will carry a spray bottle of ammonia just in case.
From a person who get them worse than others:
I am the official Pica Pica tester here. If there are Pica Pica they will find me. I don't think it is the Thimble Jelly but is the micro scopic larva that causes the problem. Although you may get a few 'stings' when you are in the water the main damage is done while sitting in anything where the larva can be trapped. As they die for lack of water they start stinging. The most important thing for those of us who are especially sensative is to get out of the suit and rinse off with fresh water as soon as possible. Since I carry a bucket of fresh water for my video camera I have been known to have someone douse me with this water while I hold my suit away from my body.
Pica Pica does not keep me out of the sea and I actually seem to be building up an immunity or getting better at getting rid of them.
For more information see this: