This may sound weird, but you should pee on it. I know, I know. I grew up by a beach, and many people got stung. If you pee on a towel or washcloth, (don't do it directly)wrap it around the area of the sting. It should relieve the sting. If this completely grosses you out, a cloth with warm water will work as well, but not as effectively.
wrap with a luke warm towel
i cant believe i got a jellyfish sting!!! it itched so bad until i want into the ocean and it started stinging. for those of you with minor jellyfish stings here is a remedie:
1) put apple cider on it not water
2) then to make the sting go away apply castor oil
3) to make the pain go away put aloe vera on it
for the itch put some hydrocortisone cream on it (available at riteaid).
hope you feel better!!!