There should be one switch for each awning. I'm guessing the 3rd awning is over the garage door, that switch should be on the overhead panel near the rear door.
The awnings are 12 volts, so look in the fuse panel, not the breaker panel. If you have enough 12 volt power to turn your lights on you should have enough to run the awnings.
Do the lights dim when you activate the switch?
If a fuse is bad it "should" have a red light next to the blown fuse.
All three awning not working suggests starting at the fuse panel and figuring out which fuse protects that circuit.
If you find the correct fuse and it is good (checked with a test light across both sides), I would pull the switch closest to the fuse panel and check the wires attached to it. Good possibility that the 12 volt supply comes into the closest switch and then runs in series to the next two awnings.