The bad news with pica pica - it doesn't look pica pica to me so it's a pretty extreme reaction - is that unlike most stings and bites where you build up a resistance to them and it affects you less and less pica pica is the opposite - it gets worse and worse over the years.

Dive skin won't help either as they get you at the seal on the neck and wrists where they get trapped. Were you wearing shorts that sort of length on your thigh to where the stings are.

Don't think its the thimble Jelly Fish larvae either - they just appear at the same sort of time