Regularity change

I have ibs, and I've been lactose intolerant since an infant.  there are certain foods with dairy I know will send me to the bathroom within an hour.  the last 5 weeks or so my regularity has changed , like I go half as often, and generally a bit constipated.  Went from 2-3 times a day to once a day, some days not at all.  If I eat dairy foods that often upset my stomach - no negative reaction.  I had a colonoscopy last week, everything normal, neg bioposies for colitis etc.  what could cause this change ?

IBS causes your bowel habits to change from one extreme to the other.  This is normal for IBS.   I have IBS and my bowel habits can change in the same way you describe. Don’t worry.