The Citizens were crowned champions on Sunday after beating Brighton 4-1 at the AMEX.
Guardiola's side finished with 98 points for the season, only one point ahead of Liverpool.
"It's incredible, 98 points, to go back-to-back. We made the standard higher last season and Liverpool helped us.
"To win this title we had to win 14 [league games] in a row. We couldn't lose one point.
"It's the toughest title we have won in all my career, by far."