I’d like to add my own guesswork to the vent situation, the usual heating and air circulation situation in a house or apartment is that you have air intakes under or near windows where you also tend to have heating, there may also be plain vents in the wall somewhere or duct work that brings air in from outside through a central heating system. But you also need an outflow, which is usually the active part in the system, kitchen and bathroom fans sucks air out in those locations creating an air flow from windows in external facing rooms to the kitchen and bathrooms.
You live in a garage which is generally not included in that system and if it is it’s as an intake. It seems unlikely to me that any air will flow from the house and into the garage unless you have an active outflow set up somewhere in there. If you do have a passive vent to the outside then it is more likely that cold air is being drawn in there and into the house than the opposite.
It could be that much of your problems could be addressed by installing an active outflow vent in the garage, which would mean the house side vent would start letting warm air into your space.
Though quite frankly with the limited information we’ve gained here I would guess that this garage is not really suited for anyone to be living in and your long term goal should probably be to get out of there.