Chop,
Im a builder..........
If it is a Moen faucet, which is a popular brand, then get a replacement cartridge at the store, and the directions will walk you thru it. Too early to be limed up. This is not uncommon in new construction. I have seen it all. Solder gets stuck in those cartridges can cause this. Also saw steel wool, pieces of plumbers tools(probably broke off in the line and the dumbasses are too lazy to get it out, I mean just look at their plumbers cracks, if they are too lazy to wear their pants right.......well you get the idea! :mj07: ) and nails in their.
If thats not it, call your builder right away, tell him what you did, and he should appreciate that you tried to take care of it yourself, and should but you #1 on his punch list.
GL
Franky