In addition to the medicines mentioned, are you a coffee drinker? Sometimes that helps. Also (this is going to sound silly but it worked for my mom when she was on chemo. Elevate your feet like on the tub if it is across from toilet.

If you don't exercise walking can assist.
And, have you been checked for an obstruction? You mentioned IBS, I'm assuming you've been tested for IBD (crohn's or ulcerative cholitis). If not, you really should and obstructions can be part of that.