Town looked on course for a well-earned point until youngster Tom Hitchcock popped up at the death to steal all three points for the hosts.
"I don't think they should have beaten us," a blunt McCarthy said.
"We just didn't do enough in that 90th minute. I thought it was going to be a good point until we didn't defend in the last minute.
"I'm pleased with the group of players I've got, but playing well and getting beaten isn't my idea of fun. We've been beaten so have got diddly squat to show for it.
"I thought it was going to be one of those days when Rob Green pulled off a save from Daryl Murphy.
"We were even with them, certainly in the first half. But if we want to contest the top six then pretty good has got to become good - we've got to get points.
"The players are bitterly disappointed, as you'd expect them to be. It's got to be a point and we haven't got one, so there's no point patting ourselves on the back."
- Sports & Recreation
- Tom Hitchcock