Patrick Schwarzenegger couldn't wait to tell his family that he was headed to Thailand to shoot Season 3 of "The White Lotus" ...

"You're pregnant," Shriver says to the person behind the camera ... but my family kept noticing me acting weird. Maria thought Abby and I were pregnant," he said, adding a crying laughing emoji.

Patrick Schwarzenegger inspired a theory from his mom Maria Shriver ... explain the off behavior, Shriver and Schwarzenegger’s sister Katherine “thought we were pregnant.” ...