Causes of ailments associated with the digestive system - what to do?

I have had bowel problems for three months. It started with a violent diarrhea, which establishes and now all the time I am accompanied by loose yellow stools with an unpleasant odor, overflowing in the intestines and sometimes epigastric pain. I took Xifaxan twice, it helped a little but after the second package I no longer felt the difference. Only nifuroktazid helps me, but when I stop taking it, the symptoms come back. Could it be a lamblia infection?