What Causes Black Coloured Stool While On Metpropol And Glocored?

I am case of post CABG 1 yr back with DM 10yrs I am on regular check ups by 3 months using medication of metpropol 50mg OD; Tab Glocored Forte BD; Tab;Volibo.0.2 OD Tab Ecosprin -150mg: Tab. clopidigril 75mgOD; and Tab.Rosvatin 20mg ; and Tab.Cobalfit OD. since 3 days I observed my motion colour was black from yellow what is reason/cause can you answer please. it is called as malena ? i observed abdomnial pain also in the evenings since 4 to 5 days