The U's had won four on the bounce back on January 12, but after going two weeks without a game due to postponements they have failed to win since.
And Wilder admitted his players are suffering.
He said: "It was a difficult evening for us.
"Their two goals have come from two throws where we've switched off.
"We're hurting because we've missed chances at times when we've gone clean through and not scored.
"It's plain and obvious to see that a few of the boys are lacking a bit of confidence, and are not prepared to do the things they were prepared to do when things were going better.
"We've got to find a way to change that.
"In training they are looking great, but they are not reproducing it when it matters."