A 2-1 defeat to the Toffees means Nuno's side are five without a win in the Premier League, while they have conceded the first goal in each of their last eight top-flight matches.
There were lapses in concentration for both of Everton's goals – coming from Alex Iwobi and Michael Keane either side of Ruben Neves' reply for the hosts – and Nuno says they must improve ahead of the big Black Country derby against Albion on Saturday.
"We played a good game, had good possession in the first half," he said.
"But in the second half, not too many chances – both teams had few chances.
"The game was decided on a set-piece which required more focus, being more aggressive in our box.
"The boys tried hard, very hard, but we're frustrated because it's happened to us too many times.
"We're disappointed because we should defend better. That's what I'm disappointed in and what we're going to work on, so we don't repeat the same mistakes.
"Conceding is a problem as the intention is always to have a clean sheet, be compact and organised.
"When you concede, it requires more on the offensive part of the game. We have to find solutions in ourselves."
Wolves did keep a clean sheet against Crystal Palace in the FA Cup last Friday but have not had one in the league since beating the Eagles 2-0 at the end of October.
Nuno's side had previously prided themselves on being solid, especially last season, but he said: "We have to stop comparing, what happened before. It's a different moment with different players, so we cannot compare.
"What we have to do is realise that we must do better in the situation that we're in.
"Defensively, it's something we have to do very fast."
Nuno's charges also lost their edge in attack in the second half. Having equalised through Neves, they ended the first period strongly but struggled to create any chances of note in the second.
The Portuguese midfielder went close from long range a couple of times, grazing the woodwork with a free-kick, but the Toffees were fairly comfortable before winning it through Keane's free header – after Wolves also did not track the run of Iwobi for his early goal.
When asked if their failure to keep going in the second half was down to themselves or the visitors, Nuno added: "Both. Everton defended very well, very tight and organised. It makes our job difficult.
"We tried a different situation which went well in ther first half. We were better offensively in the first half than we were in the second half.
"In the second half, we should do better."