Bulldogs are schedule driven and some suffer from OCD... whenever a routine changes they will react to it in some manner. Does Gunny require being crated while you are away.. can you baby-gate him in a kitchen, bedroom or another room in the house instead of being in the crate while you are gone?
Also, a possibility is sickness or pain, canines when in pain will become what seems to be aggressive, but it is a way of protecting themselves.
It may also be time to get your boy neutered there are health risks associated with keeping them intact.
I will tag some other members to provide more advice and hope we get you the right info to help you and Gunny