I just did my front pads 2 days ago - maybe the caliper retaining screws (the ones in the rubber booties (7mm Hex) arent threded right and tightened to 25Nm.
Or the spring clips on the inside arent correctly "snapped" into the cylinder...
Or the pads arent the right ones for the car...
Or the pad "handles" aren't seated in the holder grooves correctly - pull it all apart and have another go.
1hr max each wheel including tool gathering and cleanup....
Make sure you have a 7mm hex though - most sets come with a 4,5,6,8,10...and not a 7mm.....
In haste late at night I tried making one out of an 8mm but failed....it was more the haste than the skill....I'm sure of it....;>)