Hi, It is possible that the oxygen administered during the colonoscopy caused irritation and inflammation in the nasal passages, leading to symptoms such as rhinitis and eye-watering. This may be due to the dryness of the oxygen or the pressure from the nasal cannula. It is important to continue taking Benadryl as directed by your doctor or pharmacist. Additionally, you can try using a saline nasal spray or a neti pot to flush out any irritants and moisturize the nasal passages. Avoiding smoke and pollution like irritants would alleviate symptoms too. If your symptoms persist or worsen, it is important to follow up with your healthcare provider to rule out any other underlying conditions or complications. If you require a personalized response, kindly use the Ask A Doctor service and post a follow-up. Take care. Hope I have answered your question. Regards, Dr. Priyanka, General & Family Physician