The Blues have taken only two points from their last four league games to leave Di Matteo rueing another bleak November for Chelsea.
Di Matteo was rational and calm when facing the media but it is understood he was furious with his players behind closed doors in the dressing room.
Peter Odemwingie scored the West Brom winner after Eden Hazard had cancelled out Shane Long's opening goal.
Chelsea dominated for long periods but Di Matteo was unhappy with the defending for both of the home side's goals and is set to shake his side up.
He said: "It is a ground we find difficult, last season when we lost here, and now this season again. We know they are very good at home.
"But giving away goals like we did today [Saturday] makes if difficult to win the game.
"You have to score three goals to win then and our defending was very poor today [Saturday].
"We didn't concede many chances but, the ones we did, we had to do better.
Chelsea have operated an attack-minded 4-2-3-1 formation under Di Matteo but that looks set to be reassessed.
Di Matteo said: "This season we are playing a little bit different but we might have to go back (to a previous formation) to be able to win games, and make sure first and foremost we don't concede.
"Maybe it is the time where we might have to change a little bit in terms of our selection and the way we play.
"For some reasons, November for our club is a bad month and it seems the same again this year.
"We are disappointed and maybe it is time to look at things, maybe change it a bit and get a win.
"We will look at the set-up of the team and maybe sacrifice a bit the attacking options to go a little bit more defensive."
Di Matteo made five changes but insisted: "It was based on the midweek (international) games. The players were all over Europe and the world, long flights, five or six hours' time difference.
"They were not in a condition to start or last the game."
West Brom boss Steve Clarke is not allowing himself to get too excited after his side climbed into fourth position.
He said: "I'm delighted, a great three points, good attacking play, two fantastic goals, and dogged determined defensive play towards the end.
"Can we think of the Champions League? I don't look that far ahead, I look from game to game.
"It is a great time to be at the club and if the supporters want to dream a bit, they can.
"But within the camp, we will keep our feet on the ground."
Clarke paid tribute to Long after another fine performance following the death this week of his grandmother.
He displayed a T-shirt which said 'Rest In Peace Gran' after scoring his sixth goal of the campaign.
Clarke said: "I've run out of words to describe his performances this season.
"Shane produced another fantastic performance in what has been a difficult week for him.
"He wanted to play. He is going back to Ireland tonight [Saturday] to be with his family for the next two or three days."