Hi Londoner,
As someone who only got back yesterday from POP I can tell you I have more than my fair share of Mosquito bites, over 40 on one leg!
As for what works, it beats me. Nothing we took from the UK seemed to have an effect, although not everyone gets bitten so I think it is according to to skin type and how your skin generally reacts to bites.
I would wait until you get there and buy some DEET based product, tends to be more of an American product rather than one that you find in the UK. Take with you something plug product in for mosquitos in your room.
Having been to the Chemist for bites already since I have been back, they have given me some antihistermine tablets, so some of these may be worthwhile. Despite my wonderful collection of bites it did NOT ruin my hols.
Get out there, get some sun and enjoy yourself. BTW The sun in POP is very strong take good suntan lotion or get some there, the products you but out there go up to factor 70! something that we do not have in UK.
Enjoy your hols.
Leggie.