how much benadryl should i give my 2 yr old, 32lb. boy, who just got the nasal flu vaccine yesterday? And is that the best solution for his symptoms? He has no fever, just started getting a progressive runny & congested nose throughout the day today. Enough to be disruptive for his sleep. Pretty sure the symptoms of his nose & vaccine are related. Doesn't act like he feels sick or seem at all irritable. Just heavily congested nose. He's a big boy for just turning 2, so I'm little unsure on dosages on meds with him, but I always feel it necessary to remain conservative with them either way.

Optional Information:
Gender: I'm a mother of a young boy
Age: 2yrs

Already Tried:
Nothing yet. Don't like to give him meds usually, but I know his symptoms are bothersome enough to disrupt his & my sleep unnecessarily. I just want to give him some relief & easier breathing tonight for more restful sleep. Hopefully, aiding in resolve with his reaction to the flu vacc. Thank you for your help.