How do I know I'm getting enough?

I'm pretty sure I'm dehydrated and I don't think I'm getting enough food either. Typically, in a day, I'm having 4 oz juice at 8am, medium coffee for snack, 6 oz soup at noon and supper and 4 oz jello and single popsicle in the evening (both sugar free). I'm getting approx 12 oz of water as well. I just can't seem to get more than this and I have diarrea. Any thoughts?

You have to stop the diarrhea. Call the Girls in Moncton for a recommendation. You are also depleting electrolytes. Try some Gator aid for the electrolytes.
You should be aiming for a lot more water- 1.5 liters. If you can comfortably drink more than 4 oz aim for 6 oz. Try to drink something more substantial than juice, like Ensure, Carnation instant breakfast, or a protein shake. Coffee does not count as a snack- you need nutrition. You are not getting enough calories to have sugar-free jello and Popsicles. This is probably the only time you will ever hear this, but you have to increase your calorie intake! If you don't get enough calories, you risk crashing your metabolism.

How are you feeling? I tried to call a little while ago to see how you were.

You are getting less than 1000mls of fluids in per day - not near enough - I can't comment on the back door trots though. Try a couple more popsicles, broth, milk, crystal lite - try to find something you like that works for you - good luck!