After the many comments & talking to the nurse, the conclusion is that Ian had an allergic reaction to something he likely ingested. Now, what that 'something' is, we may never know. I have narrowed it down to 2 possible things, 1) bad deli turkey slices, or 2) hackberry tree berry.
I'm not even sure about the latter of the 2 but if we were outside & he found one, it may be that he ate it. I read up on them & they don't seem to be poisonous. The nurse believes we may never know for sure.
The good? The Benadryl cleared it up so quickly that the nurse said it was a mild reaction. Um. Did you see the pics? That doesn't look mild to me but then again, I've never experienced an allergic reaction to ANYTHING. Never seen hives. Didn't know what was happening yesterday when I saw his leg & butt cheeks. All I know is that I called my mom & told her I didn't think I had the stomach to be a mommy anymore.
That's how upsetting it was to me. Fear of the unknown. Especially w/ Ian. I am glad to report, I have owned my mommy-ness & do think I am good one, albeit a bit skittish at times.
Thank you all for your comments!