The striker, who arrived on a three-month loan from QPR at the start of October, is happy McCarthy is at the helm.
Campbell said: "We haven't felt like this for a while. Now we need to kick on and move up the table.
"We are all in this together - that is what the manager has installed in us.
"Mick has so much experience and he has done so much in football with Wolves and Ireland.
"With a manager of his calibre, you just know it is going to turn around sooner rather than later."