chasingtime,
You are probably reading too much into things!
I've had my pouch for 4.5 years. I have no problems whatsoever drinking without eating something, and it doesn't go right through me. The key is to listen to your body, which you are already doing, it seems, since you are drinking more and your urine is improving. Keep taking cues from your body and self adjust as needed. Obviously if you are peeing too much, cut back on your fluids, if you aren't peeing enough or it is dark, drink more. Also, your fluid needs may vary day to day so do pay attention to your thirst levels and urine output. But overall, take a deep breath and keep doing what you are doing! You are doing fine.
As for Clariton, plenty of pouchers use allergy medication without having it affect pouch function. Your biggest concern, since you are having frequent BMs, is that you may not fully absorb the meds. In that case, you should take the Clariton with food, as you have a better chance of getting the most benefit from it.