3 weeks of loose brown stool could be a lower GI infection as a strong possibility..
A case of gastroenteritis..
Most cases of gastroenteritis are viral and usually resolve within 2 weeks ( some last longer such as norovirus)
I would suggest that they might test your stool samples x three specimens >> stool culture/ leukocytes/ C.diff/ norovirus/ ova and parasites..
You could try 5 days or Pepto Bismol one dose after each loose stool up to 7 doses in a day and that may be of help..
You could have a case of IBS ( = irritible bowel syndrome) which can fluctuate from diarrhea to constipation and has increased bowel spasms and is related to stress/anxiety
I hope that this is helpful for you.
Let me know if you have further questions or concerns.
I will be happy to get back with you! '
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Thank You and Best Regards,
Anthony Bray MD