Suggest Treatment For Redness And Welts On Neck

hi, i went on vacation to jamaica,, the second day i woke up with a bad burn or something on my neck

it not all over my neck so i wasnt sure if it was a burn or not.. it was first very red and had welts on it.. then it turned purple color, and it has been over 1 month that i am back and it is still on my neck.. almost looks like someone tried to choke me.. kinda looks like a hand print..