Pompey have used more than 50 players this season as being in administration means they can only offer loan deals and short-term contracts.
But Whittingham has finally got a consistent line-up and Saturday's 2-0 win over Coventry made it 10 points from their last five games.
"It's no surprise to us that once we got a settled group together, the form would start picking up," he said.
"We've had this group of players since the Bournemouth game last month and it's taken them a few weeks to understand each other and do what we want.
"That's what it's all about - having settled players that you can work with day in, day out.
"They all worked their socks off against Coventry."