Trouble signing into email account on Gmail on Android

Hello-

For about the past year or so, I was able to send and receive my email on my gmail app just fine. Now all of a sudden this week, I got a constant error message that it "couldn't sign in", and so I deleted the account and tried to reconnect it. No matter what, using the correct email server settings for both POP and IMAP, I always get an incorrect username/password error when they are in fact, correct.