We need more information from you to analyze why you are no longer receiving channel 3.
1) First is KYW CBS3 the channel you lost?
2) What type of antenna are you using? Indoor or Outdoor? Type, make and model if you know. How much cable on the antenna to the TV? Are their splitters going to more than one room from an outside antenna?
3) Go to TV Fool and enter your address and how high your antenna is off the ground even if it's indoor, a guess is good enough. (otherwise that system puts your antenna up 30 ft in the sky by default).
4) You will be taken to a page that probably don't make any sense, but will have a bold link at the top. Copy that link and post it back here.