Too Much Water?

For months now I've been having a problem.

When I come off stage, I feel REALLY unwell - headaches, sickness, diahorrea etc and it's every week.  it usually lasts from the journey home until late the next day.

My wife thinks it could be related to drinking so much water before and during the our shows.  I'm not sure if there's any truth in this but I do drink a lot of water.  Usually around 12 x 50cl bottles over the 3-4 hours before the show, and then another 6 pints or so of water whilst performing.

I know it's a lot, as I have to pee frequently before and after the show, but could it really be the cause of me feeling so ill?

I drink so much water because everywhere I read says singers need to keep hydrated.  Also, the way I sing makes my throat pretty feel dry after 3 songs or so. 

But last weekend was truly awful, I honestly thought I would have to be taken to the hospital, I felt so unwell.  I head was hurting so much and I felt so sick - like seriously ill.

Just wondering if anyone else has experienced anything similar?

Cheers

Sean