The easiest way to check if you are shadowbanned is to go to reddit.com/user/YOURUSERNAME. If that page shows a 404 error that means the user is shadowbanned (given that there is an account in that username)
if you are sure you are entering correct info and still unable to login, Your account probably got hacked. If you had an email attached you'd have received an email on password change and can reply to that to get the account back. If you didn't have an email attached then you are out of luck
That's interesting because I did have an account there that had no activity with no email attached. The PW worked and then few hours later stopped working (I did make sure cap lock was off).