I got a red rash in 3 patches on my chest and stomach after a colonoscopy. what could have caused it? should i be worried?

Did they: Did they use any monitors on you? You can be allergic to the adhesive in the monitor pads.

Unlikely: If it was related to the colonoscopy, it is because of a drug reaction but allergies to the typical sedation medications used is uncommon. I would recommend following up with your primary care physician to get these areas evaluated if still present. They can make a more accurate diagnosis by getting your history and examining you.