For one week try removing all fruits, except banana, and continue to use white and brown sugar. Of course you want to stay away from store made sauces, confectionaries, etc.
Excess fructose acts like an osmotic laxative. It draws water into the bowel producing D. In addition when the fructose reaches the large bowel it is food for colonic bacteria. They convert it to energy, gas and other products. Some gases and the other products can act as GI stimulants or depressants producing C or D.
The amount of excess fructose than an individual can tolerate varies from person to person. Some people can handle more than 50 grams while others cannot handle 1 gram (about 1/5 of a tsp). I cannot handle 1 gram. You may be different. If you find removing high fructose foods works then you can experiment to determine how much you can handle. If it does not make a difference you move on and try something else
Here are two message ( message 1 and message 2) that I posted in a thread about l-glutamine
-------------------- STABLE: ♂, IBS-D 50+ years - Science of IBS