What Causes Delay Periods?

Helo doctor , My wife has not been having her periods for the last 2 months. The last cycle she had was on the 8th of November 2010. She undergo a CYST surgery early november. We did the pregnancy test and the result was negative. Currently she's having the pain but she's not sure whether its menstrual pain or just normal. Her stomach is currently bloated . Kindly advise what should i do....



- Sam -