Phil Edwards bagged the winner late on after Scott Rendell had cancelled out Joe Jacobson's first-half strike.
Waddock said: "We have had an awful week, it's as simple as that. We have lost three in a week and have conceded a number of goals from set-pieces and that's cost us."
He added: "Up to the last week, we had done really well. I am not looking for any excuses. We failed to deal with two set-pieces which has cost us the game.
"We have a game on Tuesday and the sooner we get a win the better and then we can kick on from there.
"We have got a good group of players here who have done well this season, we are still in a healthy position and we now need to put this week behind us."
Source: PA
Source: PA