My Child Is On Omnicef. Tonight I Gave Him Benadryl

My child is on Omnicef. Tonight I gave him Benadryl to try up his congestion. 2 hours after giving it to him he got very angry, upset and crying in his sleep. I have him calmed down but now he is having chill like systems almost like he is trying to crawl out of his skin. They are jerkey reactions every few minutes like he can't get comfortable.