you know what, just go on your vacation and have fun. take off your shirt and just enjoy yourself! too be honest i know what those pimples look like and in two days they will calm down significantly. from now on till then, (and if you can tolerate it) shower in somewhat cool/cold water to bring down the redness on your back. dont touch the pimples, they will resolve on their own but probably by the time that happens, the hair will be coming back out.
for next time that you decide to wax. take a shower before, make sure your clean and fully dried. wax under a professional, and apply witch hazel and then aleo vera GEL. Witch hazel helps in healing and bacteria, aloe vera helps to cool down redness and stuff like that. and keep applying it when it dries like maybe 2 or 3 times throughout the day. and keep the area cool and sweat free. thats all i can tell you cause thats what i do.
the sun isnt great if you pick at the pimples and leave a scar. the sun might lead to darker pigmentation. but i wouldnt worry so much, put alot of sun tan lotion and keep good beach hygiene.