You need to go back and check your work on the front brakes if that's when the issue started. If they were spongy after just replacing pads, there was no chance for air to enter the system at this point.
Check to see if when you reinstalled the calipers, the brake line was twisted. This would 100% act the way you're describing, only allowing fluid to go to one front caliper.
Also check to make sure any slides on the calipers are lubed and move freely. Check the front wheel bearings for any play.
Check to see if when you reinstalled the calipers, the brake line was twisted. This would 100% act the way you're describing, only allowing fluid to go to one front caliper.
Also check to make sure any slides on the calipers are lubed and move freely. Check the front wheel bearings for any play.