2002 Honda Accord unusual shaking

Hey guys,

My 2002 honda accord (v6) started recent;y shaking and wobbling when I started to engine (while in parking and in movement). I never felt it before, so I took it to the mechanic. He changed the motor oil, filter, etc. He didn't change or add and transmission fluid, however, I had someone else do it, thinking that I would fix the problem. He said the car was in need of transmission fluid indeed, but the shaking could be coming from one of the tires. He said two of them needed more air. I put more air, but the car still shakes, same or worse than before. It feels like Im running on empty tires, or a bumpy road. Also, Im noticing my breaks are not as reliable as before, making me feel unsafe in my "once in great performer" car.

help please.

thanks