What Remedy Is Effective To Treat A Yellow Jacket Sting That Has Lead To Swelling?

My son got stung by a yellow jacket at 10 am this morning his hand swelled to where it hurt to make a fist. He took a benadryl he said it was ichy for a bit then stoped. At 5 I had him out ice on it cause it was still swollen. Know it has swollen to his mid forearm. What now