Help! I had a colonoscopy done yesterday. Last night I developed terrible, itching with a mottled pink rash. I have had anesthesia before and never had a problem but I don't know what else could have caused this. I have taken some Benadryl but it knocks me out. I sent a message to my doctor's office but they won't see the message until Monday. Have any of you had this before? I only took a half of one Benadryl earlier because it knocks me out. I just took a whole one about twenty minutes ago but it hasn't helped yet. Have any of you had this happen? What did you do? The itching is driving me crazy.