Same thing happen to me a couple months ago when I changed my pads and rotors. I took then back off, cleaned everything, re-bled the lines, still pulled to the left when I applied the brakes. So I replaced the right caliper with a new one, bled it, and it fixed the problem. They worked fine after that.
Only thing I can think I did was I must of damaged the piston when I compressed it back in with the C-clamp.