I use olive oil. Something in the olive oil takes out the sting and helps calm the redness and swelling. It works pretty amazing. I get big welts anytime I get bit by a fire ant. If I put olive oil on it, it looks and feels like a normal little bit and within a short time I don't even feel that it is there anymore.
For wasp and bee stings, I use meat tenderizer. I learned this one from my grandmother. The meat tenderizer breaks down the protein in the venom that gets injected with the stinger. My husband is very allergic to bees and will have a whole arm swell up if he gets stung on a finger. The first time I put the meat tenderizer, he was shocked to see that his arm didn't swell at all.
Hope this helps.