Did you get a fever or anything along with the rash? I'm no doctor (although I play one on tv) but it sounds so much like sea scratch. I itched so much I ended up with a fever. Also forgot to mention that I used a cortisone cream (1% or 2% something like that) and it really helped. Don't scratch because I gained a scar from that lovely stuff. I've cought it in Grand Cayman too. I think they call it different things in different places, so it very well may be that pica pica stuff just renamed in Jamaica, sea scratch (also known as sea lice). Remember, DON'T scratch it might scar.