With constant d you're probably losing a lot of potassium. Try to work bananas and potatoes into your diet as much as possible. They're both easy on the tummy and high in potassium.
You could be anemic and/or your electrolytes could be way off, so talk to your GP and see if s/he will run some blood work for you. If they are, you can start working on that while waiting for your colonoscopy. Depending on how bad things are, and the relationship between the doctors, your GP might be able to get your GI to move up the date of the test.
You might want to try pedialyte instead of gatorade. All the sugar in gatorade can make the d worse.
Good luck. I hope things get better for you soon.