Please have your sow checked for ovarian cysts.
Sows have been engineered to be nonstop pregnant until they die young either from birthing complications or from being worn out by the constant pregnancies. That is why hormone production never slows down or stops. In older sows this can lead to ovarian cysts. Most older sows have them but the majority of cysts never causes any problems. In some sows it does however as it changes their behaviour and makes them more aggressive and grumpy because they are basically constantly in season. Sometimes a cyst can also go wrong.
A sow doesn't have to show all or even any of the usually cited symptoms for cysts to be present; this is why the majority of cysts go unnoticed.
Guinea Lynx :: Ovarian Tumors