tnvrstar, Any suggestions you might acquire, other than a conclusive diagnosis, is guessing. I discovered this nine years ago, when I developed similar symptoms for unknown reasons. It became extremely difficult for me to manage the 1-1/2 hour commute to work in the morning. I, like you, started out with what I assumed was an acute, viral infection. However, it became chronic and I began losing weight. I saw a gastroenterologist who suspected Crohns, as I was diagnosed with autoimmune disease 20-years prior. The specialist did an endoscopy and colonoscopy, which was negative, leading the doctor to believe I had IBS. My symptoms continued and I rapidly lost 30 lbs in a few months. I endured every standard GI test without definitive diagnosis. The last test the insurance companies want to pay for is the $4,000 Pillcam, which is an Israeli inspired test that employs a tiny camera held within a pill that the patient swallows. The camera takes constant photos as it traverses the length of the intestinal tract and is eliminated naturally. The Pillcam discovered massive inflammation at my jejunum (upper portion of the small bowel). Although, I do not have Crohns, the inflammation is a result of my autoimmune condition. The doctor prescribed Pentasa (normally prescribed for Crohns) and it has been a life-changing miracle.
The common symptom you describe could be a myriad of conditions. From my experience, even with all the standard tests, including visualizing with the endoscopy and colonoscopy, the realm of possibilities are endless and can remain frustratingly illusive for conclusive diagnostics through standard methods of testing. The description of your symptoms would make me wonder if there is not blood in your stool (sticky consistency whereas my description was watery). Your health issue could be many conditions unrelated to your digestive tract so I hope your doctor runs appropropriate blood work.
Good luck to you. Don't give up until you get answers. It can be a long road, but diagnosis is the only way you will know what is amiss and receive the treatment plan that will get your condition under control and your life back to normal.