Amy, it's probably a Delta faucet or a clone of theirs. With Delta faucets, you replace the cartridge. Since you are having a problem, you might shut off the water to the faucet and remove the cartridge. Take the cartridge to your home center and they should have a replacement. There are 2 different ways that you can put the new cartridge in so be sure that you read the instructions to see which is correct for your installation.