Hi. Thanks for your query and an elucidate history. The stomach cramps as a reflex mechanism. For the two functions- passing motion and urine the abdominal wall muscles have to work to give an additional pressure . Once you pass out the urine the muscles of the abdomen still feel that they need to press more = so your are getting the cramps. Here you have to undergo the ultrasonography- on a full bladder and again after you are asked to empty bladder. this is to see the residual / post-void urine after the urine has been passed. And I am sure you are going to have this more than the normal for your age. This is due to either enlarged prostate / or enlargement of median lobe of prostate / stricture urethra. There may not be an infection at all.