embarrassing question

i have changed my diet lately, but for the better - or so i thought. i drink plenty of water and i am cutting out the junk food. the only meds i take is prozac and magnesium supplements. for the past couple of weeks my bowel movements have been quite painful - it's like i'm trying to pass rocks or something. i have cut out almost all bread - would that have anything to do with it? it isn't quite like i'm constipated because i seem to be going like i always have been, it's just like i said - rocks!