It's difficult sometimes not to get sidetracked when we're looking for a "cause-and-effect". It's possible that food-poisoning at McDonald's triggered something, but at this point, maybe that search is a bit irrelevant.
I read your previous thread. In it, you seem to be concerned about wasting money on tests. IMO, your visit to get a colonic is a waste of money.
I think you need to take a long, hard look at your diet. Your symptoms sound similar to mine, before I was diagnosed with IBS and learned how to manage it. I would spend some time reading these two webpages, and try making some changes to your diet:
In a nutshell, IBS results when your system can no longer process insoluble fiber, and peristalsis forces all the food out of your system quickly. Diarrhea and cramps, bigtime. You noted the "cotton-like strings"...that's simply undigested food. All the other symptoms you noted are a result of the overwhelming amount of gas, causing your intestines to press on important nerves, etc. I spent three years in pain until I got it figured out (while battling reflux as well).
When I have a flare-up, two teaspoons of Citrucel in a cup of water is my friend. Otherwise, the dietary changes aren't a big deal. I avoid insoluble fiber as much as I can, and have a couple of servings of white rice per week. I think, for now, your visits to McDonald's are over. I used to love to eat popcorn. No more...
If the above doesn't help you, it's still valuable information you can go over with a GI doctor to help eliminate possiblities. Each time you do a little detective work, you get closer to solving your problem. With GI issues, you HAVE to be your own advocate. Doctors can only do so much, and it can take forever to get something diagnosed getting a test here and a test there...
Hope this helps.