What medications do you take? Medications can do that.
Even simple everyday GERD acid blockers cause diarrhea.
Gabapentin and Lyrica can cause bowel incontinence.
SSRIs like Cymbalta also increase serotonin which causes excess motility.

Foods too. There are many additives in processed foods, including gums, powdered cellulose, malted barley flour and malt extract, sorbitol. Some people get loose eating these.

Gluten intolerance.

Spices from the nightshade family. Paprika, green and red chilies and peppers.

Dysbiosis from antibiotic use...Candida. Kefir may help this.

Excess histamine in foods...or foods called histamine releasers.
( I have a thread in the subforum on histamine).

Fructose (fruit or high fructose containing foods). 1 in 3 people are fructose intolerant and may get loose consuming this.

Crohn's may develop or colitis. There is also a condition called Habba's which results in too much bile salts being released at mealtimes, and this causes diarrhea. You can look that up...it was on Mystery Diagnosis on TV Discovery Channel.

There are many contaminated foods out there. You could pick up something that way.

I would think that nerve damage would lead to constipation, and not the reverse. But I guess anything is possible.

There are so many possibilities I could go on and on!