things i'd drink: gatorade, vitamin water, and/or ORS (oral rehydration solution). ORS was great for being sick in africa (madagascar). just keep yourself hydrated better and watch out for yourself every once in a while.
go to the Doc...your headache may still be hanging around from all the caffiene you had. I assume you are drinking no more now and your body could be going through caffiene withdrawl. Happens to me when I drink too much and then cut it back drastically.
Water Intoxication is a real thing so don't mess around. There have been several college kids who died from having to drink to much H20 through a hazing incident.