I Am Going On A Tropical Vacation Where There Are

I am going on a tropical vacation where there are lots of mosquitos. I get an allergic reaction to their bites. Big red hives form on my neck and where ever I am bitten. I bought insect replellant, but I still need the anti-itch medicine for after the bite. What is the most effective, by prescription available? OTC creams, gels, etc. dont work for me.