Recently replaced brakes started with a squealing sound and now are making a grind noise

I just recently (about two weeks ago) had my brake pads and rotors replaced. Everything was fine for the first week or so. A couple of days ago I would hear a squealing sound when I pressed my brakes to stop. Now when I brake I hear a grinding noise instead. It happens when I get slow enough to almost come to a complete stop. And once I lift my foot off the brake and start driving again you can still hear it grind a little until I get going a little bit and it stops and I do not hear it again until I get ready to stop. I am so confused as to why they would be grinding once they have been replaced. So I know the pads are not worn already.