[type-si]

I was drove my car yesterday when I got up to 80 km/h I notice the car was shaking a bit. I didn't know my rear tire was loosing air on the right rear, I filled it up with air at the gas station and check all the tires pressure make sure they're all the same, and drove it again, it still doing the same thing. Do I need an alignment? I kept checking the tire pressure on the rear right, It goes down 7 psi in 45 minutes. Good thing I bought a electric air pump for the tire, so I can fill it up and take it to the shop tomorrow.