The England ace joined the Black Cats from Manchester City in the summer, but has failed to live up to expectations thus far.
He scored his second goal for the club in Saturday's 3-1 loss to Chelsea and admits things have not gone according to plan - especially given the club sunk into the bottom three as a result of their most recent loss.
"I haven't felt a lack of confidence in recent weeks. But it hasn't really been happening for me. It's not been happening for the team, either," said Johnson.
"It's hard to get yourself going when the team's not performing. But we've started to play well and you'll start to see the best of me as well.
"It's different from last year because it's a totally different style of play.
"I have to do a lot more, because last season I could stay high up the pitch and didn't have to do much tracking back."
Sunderland have a chance to get their season back on track as they host Reading at the Stadium of Light on Tuesday.
"The Reading game is massive for us. Everyone knows it's our game in hand and it's important," he said.
"If we play like we did on Saturday, we'll do well. We'll do everything we can to win."
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