There are a number of things that can cause this type of pain.
If the pain is more RIGHT sided (right lower abdomen) then appendicitis is always a consideration. Classically that pain is constant, tends to get worse, often starts more in the middle of the abdomen initially, then begins to localise to the right lower part of the abdomen.
Ovarian cysts can cause the symptoms, as can an ectopic (tubal) pregnancy. If your wife is having any vaginal bleeding (even if it is her "normal" period) the combination of vaginal bleeding and abdominal pain suggests the need to go to an Emergency Department and get checked for a tubal pregancy. (These can rupture which is a life-threatning emergency)
Kidney stones - can cause pain - usually one sided, often starting in the flank region radiating down towards the groin. The pain vary in intensity and becomes SEVERE in many cases.
There are a number of possible causes, some of which are serious. IF the pain is moderate to severe, gets worse, is associated with bleeding or does not improve, I would suggest the ER
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