Yes, it's all airside now. The only way to get to a lounge is using the train to the D gates. Get to the D concourse train by taking the train from the C and transferring or use the walkway near C25 -- ever way don't go down the escalator with everyone else, look for the D gates sign.
Plan for 10-15 minutes of travel time each way. The Amex lounge is far superior.