Change in Bowel Movements

About 4 weeks ago I noticed a change in my bowel movements. I've moved from a mixture of firm (never too hard) to softish (but rarely loose) stools in my lifetime to a majority of very soft stools the last 4+ weeks. I've even had watery stools/diarrhea a couple times this week and 5 or 6 times the last month. Today I felt that I passed a meal almost immediately after eating.

I'm not in pain. The coloring is normal when soft and shape is fine (#3 on scale). It's light, light brown when diarrhea. There's no blood. I'm 6-2 and weigh 230 when I should be around 200. I don't workout enough. Yet, to date, I've never really had any health issues.

I do have, by coincidence, a colonoscopy scheduled for next week that I had set up months ago as I turned 40 and lost my dad to colon cancer at 58. Yet, I'm alarmed as 4 or 5 weeks of soft and even loose stools is something I've never experienced. Although I traveled extensively in the last month, I've been home over a week and still having bowel issues.

What could be causing a month long and consistent change in bowel movements with no real change in diet?

Thank you!!