Okay, I'm a nurse practitioner in a GI department and you need to be seen!
Your symptoms can include a variety of disorders already discussed by others, but include: inflammatory bowel disease-Crohns or ulcerative colitis, lactose intolerance (not just milk and milk products involved), celiac sprue-intolerance to wheat, and many other small bowel disorders, as well as irritable bowel syndrome and pancreatic insufficiency to name just a few!
A variety of tests would help decipher your problem, breath test rules out lactose intolerance, blood tests rule out celiac disease and look for antibodies for IBD and a colonoscopy with biopsies can help confirm inflammation. A small bowel xray is useful in determining a variety of small bowel pathologies--all that can cause diarrhea.
Once a cause if found-people do very well with medication and dietary changes depending on the diagnosis.
Don't let yourself be embarrassed about the symptoms you are having, go in and talk to a GI person so you can get on with your life in a better circumstance!
Okay, I'll go back to work now and stop lecturing--lol--hope your appointment goes well.