Talk to Internal Medicine on Digestion And Malabsorption

Two years back, my urine color changed to dark yellow suddenly. My hair started falling off. I felt constipation almost on daily basis. My weight started decreasing. I visited some doctors but their medicines did not helped me a lot. Now, after two years, I have still all these problems. In addition to this, I feel very weakness. I eat healthy foods and drink enough water. But I think this food is not being absorbed by my body. My stool is very thick and sticky. Sometimes it becomes dark brown. I feel watery inside my belly. I have done my blood and urine test and both are normal. Can you please tell me what is the problem I am facing? I can feel that something is wrong in my stomach or intestines. Should I do more tests (like stool test or enzymes test)? If yes, kindly tell me the complete name of tests to be done. Thanks.