Seat a chair near the door he cries at, and call him to you every time he stops. Reward him with something super yummy that you know he loves. Do it for a while, likely the entire time he’s crying. I’d also create a set time during the day to let him out. At 5 months old he’s just at the tail-end of controlling his bladder. Every hour and a half to two hours. On the dot. Let him out, and sit with him. He probably just wants to be out. That’s fine. He’s been conditioned to whine.