Aaron Webster, Jacques Maghoma and James Collins, in stoppage time, secured Albion the second-round win over the Spireites, who scored a late consolation through Jordan Bowery.
He said: "We've been doing alright away from home of late, but we conceded two shocking goals and that made it very difficult for us.
"We just weren't switched on when they got their first goal from a free-kick situation. I'm sick and tired of it happening.
"Some things just seem to be going in one ear and out of the other. I'm going to have to react and make some tough decisions.
"I feel upset for the fans because we had a superb following and I want to apologise for a display that didn't deserve any credit at all."