I took 2 capsules of Tylenol PM about 3 hours ago to help me fall asleep (I've used Tylenol PM quite a few times before). However, I switched body washes earlier this evening and I'm having an allergic reaction to it (itchy rash). My question is, how long do I have to wait until I can take Benadryl to clear up the rash? I don't want to overdoes on diphenhydramine as that is what's in the Tylenol Pm. Any help is appreciated!