I've found that if your wearing pants designed to fit only your waist, as opposed to your waist AND the gun, you'll become uncomfortable very quick. I've ended up with some nice red marks on my hip this way from my EAA .38 snubbie digging into me. Also, if your holster doesn't have "snaps" to secure the holster to the belt and simply uses an over-the-waistband "clip" like my cheap Uncle Mike's IWB holster, it will tend to ride up and outwards every time you stand up with those tighter pants.
I've switched to a pancake-style OWB holster to eliminate this problem, since I usually wear jeans with a leather jacket or oversized shirt. Sometimes, however, I still need to dress in a fashion to where only my IWB will do. I've found that my "loose fitting" khakis with an oversized waist work well to tuck my little revolver into with my cheap Uncle Mike's IWB holster, and a 1 1/4" to 1 1/2" dress belt maintains enough tension to keep it in place while keeping me comfortable.
Another piece of advice that's already been mentioned in this thread: Wear your pants higher on the waist rather than on the hips. I'm 5'10" 160 lbs, with a 32" waist, low hips, and no butt, along with a slight gut; so I tend to wear my pants this way just to keep my shirt from coming untucked or "blousing out".
I've found that finding the right holster/belt/dress combination that works for each person can be a tedious, sometimes expensive, nerve-racking process that just plain SUCKS! Good luck in your battle.
-38SnubFan