Rory Loy put the visitors ahead after 51 minutes before a Liam Walker penalty rescued Pompey a point with 12 minutes left.
The Blues have now gone 21 games without a victory but Whittingham believes Pompey's first win since October 20 is within reach, despite watching his side sink to the bottom of the League One table.
He said: "Confidence is the biggest thing for any footballer. If they're confident in their ability and confident when they go out there with their team-mates week in and week out, they'll play better. It's improving.
"I think the players feel themselves that things are changing slightly. It's not going to be a quick turnaround when you're coming off the back of the run we've had and you're in the run we're in.
"It's a point and it's probably one we might have lost a few weeks ago and heads might have gone down after we went a goal down. So that shows there is a spirit building there."