Has anyone gave their 1yo Benadryl ?

My son broke out head to toe.

Pediatrician nurse said it was from his Roseola (he had it about two weeks ago and a rash that last 3 days and went away last week)

On call nurse for pediatricians office said: it’s untelling, probably not from Roseola, maybe his vaccines (he got his 12mo vaccines 16 days ago) see doctor in 2-3 days if it doesn’t get better or gets worse...

Well we’re on day 3, the rash has gotten sooo so bad, the hives are growing so big they’re coming together as one big welt. I took him to ER,

Doctor said: It’s an allergic reaction to the antibiotics.

He gave my LO. 3 medicines, one being a steroid, one being something sounding like Pepsi (maybe Pepsin idk) and Benadryl.

I’m worried about the Benadryl, I’ve only heard negative things about it being given to kids under 2.

Has anyone gave their LO Benadryl