Evie, I'm sorry you're still feeling so crappy. It is imperative for you to get a colonoscopy very soon. I know you're nervous about that because of your dad, but all of us on this forum have had these done at least once and have suffered no ill effects. It's really the best way for them to see what's going on in there. If they do diagnose you with inflammatory bowel disease, you will be able to start focused treatment for the condition.
Your dizzy, lightheaded feeling is probably caused by dehydration. Make sure that you are drinking a ton of liquids, no matter how much diarrhea you're having. Sometimes you just have to force 'em down. The drinks shouldn't be too sugary, though, as that tends to make diarrhea worse. I like Gatorade diluted with water by half, herbal tea, lemon water...you really need to replace the fluids you're losing.
I hope your husband understands what you are going through and will cut you some slack if dinner ends up being take-out rather than a roast! When you are finally diagnosed, you will have a wealth of information to share with him to make him better understand what's going on.
Hang in there, girl. You're going to see the doc on Tuesday, right?