Pain increasing after 6 days antibiotics

A friend has diverticulitis and has been on Amoxicillin and Flagyl for 6 days.  She has had about 10 bouts of this over a number of years.  It's Friday and she says her abdominal pain is worse today than even at the beginning.  She does not think it is due to the drugs.  The earliest her doctor can see her is next Wednesday.  They recommend she go to the ER if it gets extreme.  They did not allow her to speak with a nurse to see if this is cause for alarm.  She won't go to the ER because she doesn't think the pain is bad enough but is terribly worried about a ruptured colon if she does nothing (sister died of same).  She says she will do the ER tomorrow if it gets worse.  No fever, but she often doesn't get fever with these flare-ups.  No BM for 2 days.  Could her body be getting resistant to the meds?  Is this a substantial cause for concern?  I don't know much at all about this condition but am concerned for my friend.  Any thoughts would be appreciated.