I think the stool you are talking about is something called Steatorrhea. Wikipedia lists the causes of Steatorrhea very well and covers everything you need to know: Steatorrhea is from excess fat. Stools can float if there is excess lipid. They can appear oily and may smell especially foul. Oily anal leakage and/or fecal incontinence are possible. Steatorrhea is the key! There are a number of things that can cause it and you've got to narrow it down based on your other symptoms.
****Steatorrhea is common in malabsorption, inflammatory bowel disease, celiac disease, abetalipoproteinaemia, exocrine pancreatic insufficiency, pancreatitis, choledocholithiasis (stones obstructing bile duct), pancreatic cancer (if it obstructs your biliary outflow), primary sclerosing cholangitis, bacterial overgrowth short bowel syndrome, cystic fibrosis, Zollinger-Ellison syndrome, Giardiasis (protozoan parasite infection) or the abuse/misuse of prescribed slimming pills.
My best guess is that you would see a Gastroenterologist about this. Perhaps your family doctor could refer you. S/he may even run some stool sample testing to confirm that it is Steatorrhea.
All the best,