Lee told the Daily Express: "I hated it. Since leaving school that was the longest time I had out of football.
"When you are in the game, any time you spend out of it is not a happy time. I just found it incredibly frustrating.
"The new season can't come quick enough for me."
He also said: "My time at Bolton will certainly help me to become a better coach.
"I was very proud and honoured to be given the job and it was only heavily outweighed by the sense of disappointment I had of it not going well.
"Yes, I would have liked longer - you always do - but the facts are I got five points from nine games. I understand why I lost my job. But the Bolton fans were superb to me, my family and the players while I was there.
"I'm still fairly young and the short experience hasn't diminished my ambitions for management.
"But I am focused entirely on Liverpool now and I want to be a part of the success here."