I am 5 weeks out and discouraged that I can consume so much in one sitting. In an hour and a half car drive I drank a 9 ounces protein drink followed by a yoplait light yogurt. 30 minutes later I had what felt like constipation (sweating, nausea). I slept for 2 hours and woke up with a headache, dizziness and nausea. Maybe Im dyhydrated.

Well, the protein drink and the yogurt, which I assume was low fat and plain, are considered fluids. It is not unreasonable to be able to have them in an hour and a half. I have no idea about your symptoms.