Hello well you it's quite possible that you are getting stomach ache because of the hard stools or the constipation you are facing..You need to take at least a 8-10 glasses of  water and also take a glass of luke warm water in the morning first thing as you get up..Apart  from that you also need to have the one big banana in the night which will help in motion and also include more of fibre as greenleaf vegetables will soften stools..Thank you