Will not eating and drinking much effect my body when going to the loo?

i havent been eating alot, due to a disorder and wondered if the excess acid in my tummy and not eating alot or drinking alot would effect me when i went to the loo as i noticed that when i need to poo it hurts alot and my tummy gargles loads and makes me feel really sick, i never used to get it, and i only pee twice a day. Thanks