I just went through that exact situation.

5-6 years ago my buddy and I got violently ill on a trip to Japan. Both agreed it's the sickest either of us have ever been, and we both lost 15-20lbs each. Shortly after our illnesses went away we both developed digestion issues. Went through stool samples and colonoscopies. He got diagnosed with uc and I got diagnosed with post-infectious ibs-d. Was told all tests were fine, but life since was hell. That is up until 2 months ago when I went to the ER with an infection.

Was given 2 weeks of doxycycline and voila, I'm no longer scared to fart, not running to the bathroom after eating anything, not going 7 times a day, and having solid stools. Might be tmi but whatever this is something that I'm happy and feel incredibly relieved (no pun intended) about.

Only problem is I still have what I went to the ER for, no one knows what it is, and I have to get another colonoscopy :/