So glad I found this I'm having the same! I'm 23 and I've had so many stool samples I've also been suffering from direhea for the past 3 weeks but all infection tests are clear! What happened in the end???
I just noticed it on mine, got very scared found this page, and all of you have mentioned you got it while pregnant? Does it just happen from bowel movements? Maybe throughout pregnancy. Maybe it's just a symptom nobody's really looked into. I'm not sure.. it's weird that I found this because I actually just found out I was pregnant myself... so it would make complete sense if it were a symptom, if not anything else.
I know you posted this over a year ago, but I was wondering if it has been resolved? I am currently pregnant, only 9 weeks along and I started noticing this yesterday. I described it to my husband in the exact same way you did (black pepper specs). He thinks its food related. I'm actually starting to wonder if it has anything to do with the Prenatals. Please let me know if you now have more information. I hope you and your little one are doing well.
Probiotics actually aid and help the the existing good bacteria already in our intestines, so I don't feel this is the blame. The occult blood tests you had done would have shown "positive" if the specks were blood. They were negative, so I would relax where this is concerned. Doing the occult blood test is normally the first step in a situation like your's and unless they are "positive" for blood in the stool, nothing further needs to be done.
I was taking probiotics before I got pregnant, and I found something online that said black specks could be from bacteria die off from probiotics, but since I've been pregnant, I haven't been taking anymore probiotics, so that must not be it.
Not eating anything new or unusual.
It it were blood it would have shown up in the tests. I would look at what you're eating and see if food is the culprit. I don't feel there is any need for further testing, but if after the baby is born you can have a colonoscopy if just for peace of mind. But do look at all you're eating, and best wishes!