Why are my emotions unreachable?

Iv never really though about it mutch untill today i went to my sons grave and had to force myself to shed a tear i realise the emotions are there its like if i look inside i can see them but i dont feel them when a funny part of a movie come's on a laugh but only becouse the emotion tell my body to do that not becouse my mind found joy in the comedy when something that should make me very very sad happens my body reacts and i look normal to people on the outside but inside i dont actualy feel it i remember when i was a small child (as im only 20 now) that i felt strongly about everthing i was OVER emotional you could say even severly bi-polar if you wish but now i just dont know before my son died i could only feel extreem emotions i dident feel anger but when the time was right i could feel rage no sadness but imense dispair and now nothing i understand that its worse becouse of the trouma but what about before that why have a been so emotionaly dry for as long as i can remember.