How To Treat Severe Pain And Swelling Under The Arm Pit After A Bee Sting?

My 5 year old son got stung by a honey bee and 5 hours later started complaning of pain in his under arm pit. There is no swelling that I can see but it hurts when I touch the area and he has to keep his arm away from his body to relieve the pain. Could it have been caused by the bee sting ¿