Can colon polyps turn cancerous?

Hi doctor,

I am a 38-year-old male. Before a year, I did a colonoscopy and endoscopy due to low iron, and stomach pain. It showed that I have celiac disease and the colonoscopy was clear except with a small 4 mm polyp. It was removed and tested. It was benign. The doctor told me that my colon is clear and visible. He told me to come back after five years. I am taking a gluten-free diet for a year and my iron ferritin levels have gone from 12 ng/mL to 74 ng/mL. My vitamin D levels are normal and my celiac test has gone from 128 units to 8 units. I suffer from health anxiety and obsessive behavior disorder. I have become obsessed with checking my bowel movements with the torch of my phone and I have a panic about going to the toilet. I check my bowel movements for blood. How to have relief from this fear? My specialist told me that a small benign polyp takes a time of five years to grow and become cancerous.

Thank you doctor,

Do I need to do an annual stool test even when I do a colonoscopy every three years? The thinking of a stool test makes my anxiety worse and so I am avoiding doing it. If I do a colonoscopy once in three years, am I safe to go to the toilet flush, and carry on my day?