I've had what is classed as diarrhea for over 2 and a half days and Imodium is not having any effect. What should I do?

Diarrhea . Lasting more than 2 and half days needs evaluation by your doctor or urgent care. Any blood in the stool or abdominal pain or fever? Drink plenty of electrolyte loaded fluids.
Diarrhea . You probably are loosing lots of fluids and electrolytes. I would recommend to stay well hydrated and seek an evaluation by a family dr. .
Diarrhea. If this is part of a viral intestinal tract infection or bout of food poisoning, it is recommended that having several loose movements is ok, but after that continual diarrhea is best treated with medications like koapectate or lomotil as well as avoiding all roughage in your diet. Prescription antidiarrheal medications like lomotil, paregoric, or deodorized tincture of opium are stronger. See MD.
Go to your doctor . Two days of diarrhea will dehydrate you fairly quick. Imodium should only be used for an episode or two of diarrhea. Start drinking small sips of water every 5 minutes or so. No food. Later try some Gatorade. If the diarrhea doesn’t go away, you need to be rehydrated and look for other reasons why it’s not gone. Like a colonoscopy. You might need IV fluids. Go to Urgent Care or and ER. .