Hi. I am sorry about your father and can understand what you must be going through. Many events in our life create a long lasting impact and losing one's father is never easy. The symptoms that you have mentioned might be indicative of depression. Depression not only causes low mood, it also leads to physical problems like tiredness, lethargy and multiple site body pain. Memory weakness happens due to inability to concentrate as the mind is usually preoccupied with negative thoughts while in depression. You should get yourself evaluated by a psychiatrist and get yourself treated accordingly.