Three games on the bounce since the international break, the Lilywhites have shipped goals within three minutes of the re-start.
Blackburn netted in the 48th minute of the derby clash at Deepdale last week, while it took Middlesbrough only 55 seconds to score in midweek.
On Saturday, Birmingham scored inside the first minute of the second period.
Maikel Kieftenbeld’s goal hit the headlines because of the blooper from Declan Rudd, the tame shot rolling through the keeper’s legs.
That was the opening goal in the 3-0 loss at St Andrew’s, Jacques Maghoma and Che Adams both going on to find the back of the net.
It was a disappointing end to PNE’s nine-game unbeaten run and Gallagher wasn’t in the mood for making excuses.
“We knew going there it would be difficult,” said the 34-year-old midfielder.
“To get something we had to roll up our sleeves, battle and get stuck in.
“No ifs and buts about it, we weren’t good enough.
“That is three games on the bounce we have conceded a goal in the first two or three minutes of the second half.
“The frustrating thing was that we had got through the first half.
“We wanted to start the second half better than we had done the last two games but we conceded a freaky goal.
“I didn’t see it at the time, I assumed Dec would pick up the ball and we would be away on the attack.
“Then I heard their crowd go up, turned round and the ball is in the back of the net.”
Gallagher felt North End did not cover themselves in too much glory for the second goal either.
Maghoma got the space to twice control the ball on his chest before he turned and fired home.
Said Gallagher: “The lad chests it first time and the ball went 40 yards in the air.
“We have to react better to stop the shot, the lad finished it well but the ball was coming down out of the sky.
“At 2-0 it got really tough, Birmingham set traps for you, let you have the ball and then hit you on the counter.”