What are symptoms of dehydration?

I have a cold/stomach bug, that has prevented me from eating anything other than few saltine crackers and a sip of water since yesterday at lunch. My mouth is really dry and sticky, and white sticky stuff is forming along the edges of my mouth. I feel like I'm in a haze and I'm kind of dizzy and out of it. My stomach still hurts even after I had diarrhea last night. I Tried drinking water and eating crackers this morning, but my stomach starting hurting again and I feel nauseous--like Im about to get diarrhea again. I'm currently sipping diet 7up, but it is making my stomach hurt. I'm home from school and scared I might be getting dehydrated. What do I do?!