What cause to run rough.i wastold i have a bad transmission mount on leftside

Honestly, i dont know what is wrong. I do know that the check engine light is on and when i had my cousin who is a mechanic do a oil change and change the spark plugs he told me that i have a weak transmission mount. Also, while im driving i can tell that it is running rough, and to me it seems like it is not shifting right or it is shifting rough. My cousin also told me that i should get scanned because places like autozone only have code readers. if and any help will be greatly appreciated. I love my car!!

He is exactly right, scanning is the best method of diagnosis we have in the industry. That would be good for your misfire, however, the misfire may not be causing all of the vibration since the transmission mount is known to be failing.