I had a problem that sounds similar. I would feel terrible unless I was drinking tons of water, but then I was using the restroom *constantly*. It felt like it all went straight through me. I started running in to electrolyte problems as well.
The following has been (extremely) helpful for me, but, as always, talk to your doctor before making changes. I started out with pedialyte, but it has more sugar than I want and really adds up at $3.50/liter. This costs me about $0.20/liter.
UNICEF and the World Health Organization have a recipe for fluid replacement that they use for dehydration. It has saved a bunch of lives in the third world.
2.6g sodium chloride (table salt)
– I use “canning and pickling” salt because doesn’t have iodine or anti-caking agents. Should be available at the supermarket.
1.5g potassium chloride (salt substitute)
– I picked this up from amazon.
2.5g sodium bicarbonate (baking soda)
– I use Arm and Hammer, again from the grocery store. The new recipe listed on the site uses trisodium citrate, but they mention in the paper that the change was only made because it stores better in tropical climates. I make up my drinks immediately so baking soda works great.
15g glucose (dextrose, corn sugar)
– I picked this up off amazon as well, but you might be able to find it locally. You might be able to use table sugar (sucrose) for this as well but the amount *will* be different so you’d want to look it up.
1 liter water
– Easiest ingredient of all.
Put it in a bottle and shake well. I drink two liters of the stuff a day (compared to the gallon or more of straight water I was drinking before), feel better, and bathroom times are much improved; your mileage may vary.