The run of poor form has left the reigning champions sixth in the standings with 31 points from 19 matches, 14 fewer than leaders Liverpool, who have a game in hand.
City's campaign has been hindered by a rash of injuries, with Ballon d'Or winner Rodri, goalkeeper Ederson, as well as defenders John Stones and Ruben Dias among those sidelined.
"There are many, many things and I missed something - something I am not doing well," Guardiola told reporters ahead of Saturday's home game against 13th-placed West Ham United.
"In the end, when you lose a lot of games, it is an incredible responsibility for the manager to take. There is something the team needs and confidence, and I was not able to do it.
"The call is on me first, it's not the players. They naturally drop a little bit and that is normal. It happened a little bit last season as well.
"I blame (myself). It's not to say, 'Oh, how nice is Pep' - it's the truth. I lead that group of players and I could not lift them. This is the reality."
Guardiola's side will look to make it two wins in a row on Saturday after beating relegation-threatened Leicester City 2-0 last weekend.