Tagamet/Zantac for wasp/yellow jacket stings?

I was stung by some little #@&! about 24 hours ago. The area is red, hot, swollen and painful and measures about 14×10 inches on my thigh. I have taken Claritin (H1 blocker) and Advil….was told to add above (H2 blocker). What is the physiology explaining the addition of this medication? I realize that H1 and H2 are both histamine receptors. I cannot find the exact mechanism of action explaining how an H2 blocker will help w/ symptoms typically associated w/ H1 receptors. Thoughts?