2006 Pontiac Torrent Brakes

1 year ago, had brakes done. No problems but brakes were original, so first it was new shoes. Then after the fact said we needed new rotors. Mechanic put on rotors. Didn't "feel" right. Car was shuddering on our trip to Florida. Took to a local mechanic. Put in a sensor. Seemed to be okay. But never felt as they were prior to having the brakes looked at in the first place. Just 2 weeks ago. After driving to a local park. The drivers side wheel was billowing black smoke and smelled really bad. Took it into shop. Had all new brakes pads and calipers on both sides. Today smelling a bad burning smell again. Mechanic on vacation this week. What can be the issue?