I think i finally got it, im new to Unreal so it was a newbie mistake as i expected. So i read this in the doc : “Whether this Pawn’s input handling is enabled. Pawn must still be possessed to get input even if this is true.” (https://docs.unrealengine.com/latest/INT/Programming/Gameplay/Framework/Pawn/index.html).
I was trying to get my input from Pawn blueprint instead of from the Controller blueprint of the Pawn.