Other than making an appointment with your Dr. as soon as possible, take some "Imodium", this will help.
Start the BRAT diet, this includes: Bananas, Rice, Apple Sauce and Toast.
Other than Probiotic Yogurts, DO NOT eat any dairy products, it will just make it much worse.
You should be tested to see if you are Lactose Intolerant, if you have Irritable Bowel Syndrome, or any other Bowel Diseases.
Also make sure that you drink plenty of fluids to stop you from getting de-hydrated.